Why do some DM's (Dungeon Masters) from Dungeons and Dragons not allow players to play evil characters?

Every DM has their own reasons for allowing or not allowing that.

I avoid D&D itself as much as possible, but in other RPGs, I typically have some idea of the range of player characters I’m interested in supporting. And if there’s more than one, whether or not I want them to have a chance of getting along when they meet and/or try to do anything together. Unless all the players characters are coordinating to get along, then an “evil” character is more likely than most to lead to discord between the PCs sooner or later, possibly immediately. Sometimes that possibility is ok or even intended, but often not.

But even if one tries to indulge evil characters, even one PC acting by themselves, it tends to lead to a fairly different, often unpleasant, type of game. The last time I really indulged such a request, in doing the preparation for the game, I ended up changing my mind and deciding not to do it, because it ended up being such a horrible situation that I stopped being willing to run it, before we even really started playing.

Another consideration, getting back to D&D itself and one of the many reasons I avoid it, is that “Evil” characters don’t really make a lot of sense. They tend to be a poorly self-consistent conceit, which becomes more apparent the more one engages it. That bothers me, though people willing to play D&D must necessarily have a certain tolerance for nonsense. But for example, to roleplay an Evil character, the question naturally arises “why is this person “Evil” – what’s that really about? That’s an interesting question to me, but I find D&D’s premises and ideas about that fundamentally unsatisfying.

On the other hand, roleplaying characters who do make sense to me, and who end up doing quite a bit of evil, but in ways that make sense to me, can be very interesting to me. As long as it’s in an RPG system that interests me, e.g. GURPS.

@Zaku Oh thanks. I thought it was for ethical/moral reasons.

Well again, every DM has their own reasons, so for some, doubtless that is it.

I’d guess (well, from experience reading RPG forums) that more common D&D DM answers are things like:

* “Because it’s annoying”

* “Because the games I want to run assume the PCs are not evil”

* “Because I and/or my players want the party to cooperate, not kill each other, and an evil PC among them has them turn on each other, and/or puts us in a problem because we agree to cooperate but it doesn’t make sense, etc.”

* “Because I don’t really know how to handle that”

* “Because my players do annoying things then some of them are evil”

Etc

@Zaku Thanks for elaborating on your answers.
Thanks for the white space and very coherent answers.
I used a cheat code in Baldur’s Gate 2, and killed everyone in town. It gets old quickly.

In real life all life would be slime and destruction. Like when Raistlin, the wizard from the DragonLance novels, killed all the gods evil and good and all was slime and death.

Well that’s another problem I have with D&D. The power scales between various creatures and magic are so steep, and normal humanoid society is so far down on the weak end of it, that yes, unless the DM creates their own campaign which only includes certain very restrained creatures and monsters, and few people who are allowed to become high-level anything, then logically, the power dynamics would be crazy, and there would be not much PC zero-to-hero going on.

@Zaku ^Agreed.

Depends on the DM. Generally, most campaigns, especially most pre-made campaigns, are aimed at a heroic outcome. A player telling you he wants to be evil is pretty much him announcing he wants the freedom to f—- up your campaign. Without morality to limit a character, especially as they climb levels, it’s hard to justify the ‘town guard’ being 10th level or someone else that can limit them. Morality is the limiter.

Campaigns focussed around evil character are rare and require a smart and capable GM.