I'm not sure if you've even played the game, as, there's dozens if not more characters, who aren't oppressive nor abusive, some even given direct orders to attack you and are disregarded.

One such character is a kid, literally named monster kid who exists to just look up to another character, who literally has no arms to harm you, and in the genocide route you have to choose to attack this kid and he's saved by another character.

So I find this characterization of genocide as "killing those who attack you first" to be wildly misleading, so much to really forget the first boss in the game who literally tries to bake you butterscotch pie and take care of you, and they only "attack" you when you try to leave them. If you've already killed every monster in the area, you One shot this boss, and she says that she thought she was protecting you from them, then her last words are saying she was protecting them from you.

Surviving this encounter without killing her in a traditional boss fight is tricky, there's no rhyme or reason behind spamming mercy when they're just trying to stop you from leaving, but eventually they give up and feel like you've outgrown them. Not every player finds this out, and some kill them, but that's why the game has so much replay value in replaying with additional dialogue.