His existence is justified by the fact that he was included in the game. Sorry you don't like the character, you're free to just leave him at the camp or murder him at the start of the game.
You described two extremes as examples of parties he wouldn't fit into, but conveniently left out neutral groups. God forbid if we have nuance and humanity in our playthroughs by being more complicated than the hero or villain archetype. I have him in my party because he's a rogue, and his ability to assassinate people and pick locks helps me focus on not doing those things.
It just seems so harsh to distill his character down to "creepy rapist", especially without even scratching the surface on his backstory.
I would imagine a vampire would sneakily attempt to drink my blood at night. That's kinda their whole thing. How that equates to being a rapist is beyond me.