Why is killing monsters evil?

Why is killing monsters evil?

It's not and you should ignore anyone who says it is.

It isn't.

Wrong question. What you should be asking is "When is killing monsters evil". The answer is "When more humans than monsters are killed".

When SJW make a game.

It depends on the setting. More specifically, why "monster" is defined the way it is within that setting.

A "monster" includes beings of pure good in Dungeons and Dragons for example, like unicorns and gold dragons. Wakfu defines a monster as "everything that isn't the PCs". In Warhammer Fantasy, "monster" means "anything I haven't seen before" in-universe, and anything big that doesn't like to march in formation in the meta.

Why is eating humans evil? Monsters gotta eat.

Killing humans is immoral.

Why do people care about pretentious indie games?

This.

It's bad in settings like Undertale because "monster" is everything that isn't human. Killing monsters just because they're monsters is evil because you're killing non-evil beings that happen to be non-human. Killing "actually evil" monsters isn't necessarily evil though, depending how liberally you apply the label of "actually evil."

It's good in settings like Castelvania and most other old vidya because the monsters are actively hostile not just to you but damn near everything; they're unwilling/unable to negotiate and actively genocidal.

It's neutral in settings like Monster Hunter because monsters are just big animals. Sometimes you've got to kill them for food or resources or because they're a threat to humans/the local ecosystem or just because you're getting paid and you gotta eat too.

As for settings where monsters are actively aggressive/genocidal and unwilling to negotiate and you're *still* painted as the bad guy for fighting them, that's just faggots trying to be subversive but failing.