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 and a tad too demanding a tad too quickly.
An evil character doesn't mean stupid or cruel. This means that he can also be manipulative and smart, and not just shred everything in his path... You probably didn't think about that.
Again, I don't see Astarion's bite as an evil or terrible act.
