This is the weirdest take I've seen on Astarion...
He's not part vampire, he is a vampire. He is definitionally an evil, undead monster.
But also, he's not a rapist. He never rapes anyone in the game, and he never tries to rape anyone in the game. When he flirts with you, if you turn him down he backs down immediately and accepts that no means no. Hell, when he tries to bite you if you say no he backs down immediately and accepts that no means no too.
You're also given plenty of chances to kick him out of your party and to even attack him, precisely because he is an evil undead monster. For Astarion to hang around, you have to explicitly allow him to do so.
Call him a monster, call him evil, but comparing him with a rapist is just so far out there and makes no sense at all.