There's a line between a "gritty, realistic setting" and "help people role-play the worst elements of humanity."
In Fallout 2, sure, it was possible to become a slaver, but it's not like they gave you broad, detailed storylines allowing you to mastermind the systematic and targeted capture of a class or race of people for sinister purposes.
I take the point. If you can walk up to someone and stab them in the face, is raping someone really much more of a leap?
But... yeah, it kind of is. Combat's a pretty well accepted game mechanic and serves a specific in-game purpose: loot and xp. What purpose does rape serve in the in-game setting? Realism? I guess, but... I mean, child molestation happens, but it's not a teenage male power fantasy usually, and I don't see anyone clamoring for that for the sake of realism. :/
I'd kind of prefer that if the game touches on rape scenarios, then it should offer them in the context of third parties. Like you can let the raiders keep their sex-slaves if you're cool with that morally, or you can kill them and rescue them, or maybe even kill them and romance them, but killing them to rape their sex slaves feels like it crosses a line somehow.
Would you want to have to write that dialog?
"Thanks so much for saving us!" "Well, about that..." "..."
Vault Dweller: How about you and I... well, you know... get together.
Tandi: I'm not that kind of girl, mister. Go find a Brahma or something.