The main defence to the companions behavior is that they're realistic, that's what i was talking about. The evil path is also just bad, nothing to do with realism.
But again, i don't see how any kind of evil character wouldn't have a problem with a chaotic evil out-for-myself vampire who first assaults them and then tries to suck on them(and possibly kills them), all in the course of a couple of days. I guess if the player likes him excuses can be made, which admittedly i did too when Gale started getting a tad too clingy a tad too quickly.
Because Astarion actually wants to work with you and he really isn't chaotic evil. He is not an insane "lol lets kill people randomly and damn the consequences" kinda guy, he has a plan, and he follows through with it. He sees you as important to his plan so he works with you and he is even trying to be not entirely unpleasant to you.
