He's also pretty devoid of empathy for anyone he personally doesn't like. Encourages murder and torture constantly, approves of you backstabbing people and fucking them over, and is generally kind of a dickbag.

All the characters are well-written though, because they're all multifaceted like this, and deeply flawed. Both of these assessments of Astarion are true, I think. He has good reasons for being the way he is, and if he's nudged in the wrong direction he easily becomes just as foul a monster as his master was. Nudged the other way, he learns to mellow out a bit and accept that he doesn't have to hurt people before they hurt him.