I'd probably be too self-conscious to play a bad character with other players in a DnD type of thing, but I've definitely done stuff like dark side runs in Knights of the Old Republic and see no harm in it. For the most part, in those type of games, the evil is so over the top that it almost loops around to being comedic. Like "rah you looked at me wrong, I'm going to be evil to you!" Though to some extent, life experience colors it too. Like I most played that stuff when I was less informed on the world and knew less about how it works.

Nowadays when I play a video game where violence is the norm, it doesn't matter much whether it's an "evil" playthrough or an (allegedly) "heroic" playthrough, I can't help noticing just how many games rely on this implicit design where it's fine to murder hordes of enemies, while sometimes having stories with moral qualms about whether you should kill a significant named character. It's the same superhero logic that Pete Holmes makes fun of in his "Badman" (parody of Batman) sketch, the one called Batman vs. The Penguin. "My one rule is I don't kill," then he takes out henchmen without a second thought.

I find the inconsistency of it to be impossible to unsee and that more than fictional good/evil character choices is the part that stands out to me. Typically in games with a hero or villain playthrough option, the heroic path also involves murdering lots of enemies along the way. The net kill count isn't actually that different. The main difference is whether you do the story-based good/evil cinematic choices, which often involves an impact to the game world that you don't even visibly see. So you're largely playing as a hypothetical hero or villain, removed even from much of a simulation of consequences.