This just keeps confusing me every time.

Dragon Slayers: originally thought to be mages who have special magic designed to work against dragons.

However we then learned two things:
1. Dragons appear to be extremely resilient towards everything BUT Dragon Slayer magic.
2. Dragon Slayers slowly turn into dragons if left unchecked. Process accelerated if they actually kill dragons and absorb their power (Dovahkiin, dovahkiin).

I had my suspicions about Dragon Slayer magic from the very beginning, but this basically confirmed it for me. Dragon Slayer magic is magic which isn't about defeating dragons, it's about becoming a dragon. Dragons appear to have a heavy resilience towards nearly everything, as seen in the one arc that they showed their face en masse. Dragon Slayer magic doesn't so much deal twice the damage to dragons as that dragons have a 50% damage reduction on every type of damage dealt to them and Dragon Slayer magic ignores that damage reduction.

And the reason why magic that makes you like a dragon would make you able to fight dragons is also pretty obvious: the biggest enemies of dragons are other dragons. They would constantly fight for territory and the like. Most of the time with powerful creatures their biggest enemies come from their own kind. So dragons throughout the ages would fight each other, and eventually the ones who managed to develop their magic in such a way that they actually could ignore that damage reduction flourished while the rest died out. That's why Dragon Slayer magic, which gives you the magic of a dragon, actually allows you to stand a chance against a dragon's ridiculous resilience.

Enter God Slayers and Demon Slayers.

Since they are also called Slayers and in general seem to act the same I'd expect them to be the same as Dragon Slayers. God Slayers have magic that makes them divine beings (gods standing at the top), Demon Slayers have magic which makes them demonic (demons at the very bottom since hell works upside down).

Instead on this site God Slayers have their magic infused with vileness (=unholiness, I just call it vile), and Demon Slayers have a holy infused version.

Dragon Slayers become like the very things they're supposed to Slay because aside from other supernatural beings likes gods and demons, the easiest way to be as strong as a dragon is to become like a dragon. But God Slayers and Demon Slayers seem to be doing the exact opposite. God Slayers hunt Gods, but their magic is vile. Demon Slayers hunt Demons, but their magic is holy.

The result is that Dragon Slayers appear to be fundamentally different from God and Demon Slayers, in a way that the God and Demon Slayers are similar. We have by far the most knowledge about Dragon Slayers, so I'm inclined to believe that this isn't because Dragon Slayers have been incorrectly explained.

Then there are some other problems, which go as follows:

God and Demon Slayers can eat every form of their respective element, merged with another element or not, except that which comes from their counterpart. In other words, a God Slayer can eat all types of flame except the holy flames from the Demon Slayer. Likewise the Demon Slayer can devour all the earth except the tainted earth of the God Slayer.

Let's assume that God Slayers and Demon Slayer at least still follow the idea that you turn into some kind of supernatural creature to fight supernatural creatures. So they share at least that similarity with Dragon Slayer still. Honestly if we were to remove that I'd have to wonder why Dragon Slaying magic would still be put in roughly the same category as the other two, if even that wasn't in there any longer.

Seeing how Demon Slayers use holy magic and God Slayers use vile magic, and I'm really hoping we're not going to resort to the claim that demons are actually holy and gods are unholy because that just sounds like an excuse to make this place extremely grimdark and edgy as hell, Demon Slayers become like gods and God Slayers become like demons. That would also explain the whole holy and vile confusion.

However, if that's the case that means that a Fire God Slayer actually wouldn't be able to eat the holy flames from a Fire God. Since Fire Demon Slayers use holy flames, and saying 'the holy flames from a Demon Slayer are sufficiently different from the holy flames of a god on a fundamental level' sounds...well, honestly it sounds a bit like an attempt to explain away the problem with the current system. It isn't something I'd expect to hear if this system wasn't already in place and we were still working on setting it up.
And the same counts for Demon Slayers the other way around. The only type of their element that they can't eat is most likely going to come from those very things they're supposed to Slay.

And in case the argument comes up that not all gods are holy and not all demons are vile, yes, true, but in general you can assume that god=holy, and demon=vile. In modern culture lots of people from all over the world have joined the idea that demons could be just as good and pure as a god and they're just tragic heroes, while on the other hand a god can be worse than the devil himself, but all in all, they're called gods because they're the strongest representation of what is holy, and they're called demons because they're balls of raw vileness. Exeptions aside, that's what you can expect when dealing with them.

Last problem I'm seeing:
Dragon Slayers learn their magic from dragons. Preferably. You could probably just write it down and share it, but in general it's dragons. Which leads us to the question:

Where do Gods and Demons get the ability from to teach their mortal students their elemental magic, but with the exact opposite element? What's the trick a demon uses to teach a mortal to use Holy Ice instead of Vile Ice?

Sounds a bit weird to me. One of the explanations I've heard so far is that Demon Slayer magic is from a demonic source but purified, and God Slayer magic is from a divine source but corrupted. But then I have to ask the question: wouldn't it be a lot easier if God Slayer was from a demonic source without it being purified? And Demon Slayer magic from a divine source and untainted? It'd basically mean you're skipping a rather large step in the process of acquiring magic, a step which quite honestly would only be there to justify the fact that the elements seem to have been switched around. It isn't like demonic magic would be that easy to purify, or visa versa.

Okay, so after all of this, I just have one thing to ask:

Can we please just switch the names Demon Slayer and God Slayer around? It'd pretty much fix all of the problems and be a whole lot less confusing.

I mean, yes, technically it is possible to alter the way stuff works around here in such a way that it makes sense the way it is, but that would feel a lot like covering holes up after drilling them instead of actually filling up the holes.

There are three things I can think of that might make the current system work.
1. Gods are now generally vile and demons are holy. In which case, why are we calling the gods gods and demons demons. You might just as well call the demons gods and the gods demons, since holiness is by definition part of divinity, and vileness is inherently part of the damned part of existence. You'd have to completely disconnect holiness and vileness from the sources they have in nearly every setting you can name which isn't purposefully making a mockery of the whole thing, and attach them to the other source just to support the current naming method.
2. Somehow, through some mysterious means, it's significantly easier to get purified demonic magic and tainted divine magic over demonic and divine magic in their natural form. This doesn't have quite the same problem as the first one, namely that you'd be confusing the hell out of people, but it's still a bit like 'we're doing this more to protect the status quo than that it's actually a good idea.'
3. Demon Slayers and God Slayers somehow use holy and vile magic respectively, but their version of the holy and the vile elements are different enough from the ones used by gods and demons that a God Slayer can't eat a Demon Slayer's magic but they CAN eat a god's magic. This, once again, sounds more like an attempt to defend the current situation than that it's useful or that it makes a lot of sense.

Of course I only have one perspective, so I could just be looking at this completely the wrong way, but all in all the only explanations I can see for why we'd keep the names as they currently are would be focused more on the idea that people don't want to bother changing the names than that it actually functions as an improvement.

Personal suggestion, switch God Slayers and Demon Slayers around. Suddenly it all makes a lot more sense and doesn't require confusing explanations for why they're so much different from Dragon Slayers. And Dragon Slayers are, once again, the most solid Slayers we have in regards to information, so if somebody suggests changing those to fit the other two I'd have to responses:
1. That would be some real strong determination to let Demon and God Slayers keep their names, so much that you're actually willing to make things even harder by trying to change the rules regarding the Slayers we know the most about, and
2. What's the opposite of a dragon. I mean, I'd argue turtle, but then you'd have to add Turtle Slayers. Like seriously, what.

P.S. I welcome any and all good attempts at helping me understand why we don't have to switch the names around. However I'll be asking everybody who posts here to not do anything which might cause drama. Examples: act offended because I took one of your personal explanations for the status quo and explained how I think it doesn't make sense. I'm sorry if I offended you, but I'd rather you explain in a reasonable way why I'm wrong than that you act offended, since that just creates drama. Which nobody wants. Next example is making it personal. Or name calling. Or saying I'm being whiny about this. I mean, you can say that you don't think it's that important, but there's a big difference between 'I don't think it's that big a deal' and 'stop making such a big fuss about nothing, you baby.'

P.P.S. In the magic rules section they talk about God Slayers using darkness and Demon Slayers using light, instead of vile and holy, but that darkness infused stuff deals extra damage to basically everything considered holy and the light infused stuff deals extra damage to everything which is usually considered vile, so I'm just going to keep everything here focused on the terms holy and vile because that's basically what we're talking about.

The demon and god slayer magic on this site were made before it was introduced in FT. The site also is non-canon, meaning it does not have to follow the rules of the show at all.

A god slayer uses a magic that the gods are weak against. You wouldn't use holy magic against a holy being. A god teaching you to slay other gods would teach you as much.

Swapping names wouldn't help out any. You'd have demon slayers using unholy magic, when they themselves are unholy beings and vice versa for the God slayer.

Try not to look at Fairy Tail and compare the site to it. It will lead to confusion. Non-canon allows more freedom for ideas and tends to allow a lot more leeway than being canon and having to go by what the show does for every little thing.

I'm not so much following the rules of canon as much as the rules of what I think makes more sense. Also I already have seen several examples of Dragon Slayers who follow the idea that Dragon Slaying magic causes you to be more like a dragon on this site.

Actually using holy magic against a god would work following the same idea as Dragon Slaying magic does: you can eat their magic, use it for your own, and most importantly, it allows you to fight them on even footing. That's how Dragon Slaying magic works, and I don't really see why it wouldn't work for Gods and Demons.

And swapping the names would mean that all three the Slayers now all follow exactly the same basic rules: they become like the very creatures they're hunting to be able to be an even match. It'd mean that the only difference between Slayer types is what they hunt and turn into, in contrast to now where Dragon Slayers follow fundamentally different rules than God and Demon Slayers.

Once again, not following canon rules. This is just me looking at the rules for Dragon Slayers both canon and non-canon, including how people on this site believe Dragon Slaying magic works (so non-canon), looking at God and Demon Slayers and seeing a rather glaring difference of which I know that I'm not the only one who finds it confusing.

And I don't think this classifies as a positive result of more freedom. It is a result of freedom, but while freedom can allow for creativity and cool ideas it can also cause stuff to happen which in hindsight turns out to be a rather strange or bad idea.

The argument I'm making is that the current situation is a negative result of freedom and that we should change it, even if that might be difficult for some people to accept because people are naturally inclined to keep the status quo when possible.

Mostly we believe it is 'vile' or 'unholy' due to its black colour and I believe either in the manga or anime it was described as 'evil' feeling. Not 100% sure though.

Just going to point out, that in a sense the god/demon slayers do sorta follow the cannon, as the Flame God Slayer in the show has shown to have black flames. ._. Just let it be really also. You realize the amount of people you'd mess up with this change? A few people have plot based around their characters magic being what it is.

That is true, but as Aiyana just said, this site isn't canon and doesn't have to follow the exact same rules.

I could make the argument that the current situation is actually more an attempt at following canon even though it might not be a good idea, than my idea of swapping the names around.

@Kiku I've let it be for a very long time, but I figured that I might as well try to see if I can get that confusion out of the way, because I'm pretty sure I'm not the only one who looks at the current situation and makes a face.

And yes, it might inconvenience some people, but every time that the rules around magic change there will be at least a couple of people who learn that now suddenly they have to rework their magic to make it follow the new rules. This is just my opinion, but I think clearing this up would in the long run not cause that much trouble and at least make all the Slayers the same on a fundamental level.

Eh. To be honest I think they are fine the way they are.

I never personally thought of it as holy and unholy or good and evil.

Its just a different type of magic. IT makes sense for holy magic to be super effective against demons and in traditional christian mythos demons are just fallen angels and in other mythos they are dark gods. So....it wouldn't be too far to say that they don't have knowledge of holy magic enough to be able to teach someone it to wipe out fellow demons.

As for gods...well...its seems pretty 'corrupted' as I like to call it to slay a god. Hence the black colouration and evil feeling of the magic.

I don't see any need for this change.

That is, of course, one way of looking at things.

Although for the God Slayer part, wouldn't that then only become corrupted after you've already killed one divine entity?

I personally don't agree with the whole God and Demon slayer thing, I think they're fine where they're at. But I do ask: what exactly about Dragon Slayer Magic makes it so special to deal double damage against such savagely powerful creatures?

God and Devil Slayer Magic each have this kind of different color and shade to it, as well as given certain attributes that cause them to deal double damage to the opposite; it makes sense. But why does Fire Dragon Slayer Magic deal double damage against dragons and reptiles? It's just...fire...that's it. All a Dragon Slayer can essentially do is consume their element. Their fire, ice, wind, water, etc. have no actual statistics to them that would give him an edge against dragons.

I don't have much of a problem as to why it exists, my issue is the explanation; in the anime, the explanation is that all along it didn't. There was nothing special about it. But what's ours?

The explanation I have for that is I admit a bit of a stretch, but it's about all I could think of.

Spoiler:

Tl;dr: Dragon Slayers don't deal extra damage. Everything else just deals less damage to the dragons and Dragon Slaying magic is basically dragon magic used by non-dragons. Dragons can harm each other because when fighting the ones who actually could kill the other dragons would survive and pass on that ability to their descendants.

EDIT: might not exactly be a thorough and satisfying answer, but I've thought about this for a pretty long while and I honestly didn't get any better ideas after I found this one.

Main thing is that even if it is a bit weird or confusing is that changing it could break a lot of people's magics. Some people might have built their god slayer around the vile/corrupted nature of it or a water demon slayer might have built it around the 'holy water' aspect which totally works for me and is pretty awesome.

Heck if I was an earth demon slayer i'd focus on rock salts and maybe crystals for focusing light or something.