About Astarion: yeah, he is clearly evil, for reasons Sozz, Tuco and others have stated, but I also had one conversation with him where he stated 'Killing is fun'. That sounds pretty evil to me.
I don't think any reasons were actually stated. It all seemed to be foregone conclusion and presumption of motivation.
The dialogue shown was something that could, at best, be read into. Astarion says you didn't do anything to save Arabella. Okay. He's pointing out your inaction, somewhat ribbing your conscience. It's also a game environment where there's a meta aspect. In normal life, you could reply, "You didn't do anything either!" But obviously Astarion couldn't do anything being under Tav's control.
As for the drinking blood stuff, Astarion doesn't actually drink your blood without your consent. He clearly intended to, but he didn't. Regardless, given all the context and history, I don't see how that marks him definitively as evil.
