I do not see Astarion as necessarily a bad person, as his actions are mostly driven out of fear of Cazador rather than his ambitions. His search for power, not liking wasting time on helping peasantry and such are all the result of his fears because he under no circumstances wants to return to him as a slave again. It's why he is so jumpy all the time and has outbursts.
He did afterall spend the last 200 years being tortured and starved on a daily basis. That kind of mental and physical torture would mentally break people, so if anything I admire Astarion for keeping his sanity and remaining semi-decent. No denying he is changed slightly for the worse and self-centered, but realistically that kind of torture would create a murder hobo who would never trust anyone again. Like a badly mishandled dog that bares its teeth at anyone who tries to approach it with love and care because it no longer trusts humans. Yet with time they grow to trust once again.
So I see him just as I saw Sebille. An innocent elf taken against their own will through clever machinations and enslaved to be used as a tool to do inhumane things. Who naturally end up broken by it, but by the end they get their redemption arc and become great people again.
Or just like Visas Marr in Star Wars KOTOR 2. A pure force user and only survivor of her race, taken and corrupted by Darth Nihilus who Meetra Surik later saves. Visas becomes once again a pure force user with proper hope and ideals and after the story she brings back her dead wasteland of a planet back to life with the force.
I also do not see Lae'zel as bad either. Considering her teachings and culture, she is actually doing splendidly all things considering. Like her remarks about her cutting our tongue out for interrupting her or skewering Zorru. People might think of these as shallow jokes or threats or think it is her personality speaking, but they in fact show her morals by breaking protocol and Githyanki customs. By Githyanki standards she is quite merciful, respectful and nice and gives us leniency when it comes to not understanding her. She even grows to like us and admire us as time goes by, especially if we take interest into her culture. Not to mention she already in Act 1 starts seeing Faerun slightly different than when she first arrives.
So yeah I honestly do not think any companion so far is evil or bad. Minthara might be the only evil one, but I doubt she might be fully because she is afterall controlled by the Absolute and doesn't know it.
What I am trying to say is; people can change. In Larian games though, some start as douchebags and slowly become fantastic likeable people that are like family be the end of the game.
Honestly, I think the real problem is the idea of evil itself. I think it is better to think of "selfishness" than literally "does the character murder cute puppies". Whenever we think about evil in the real world as truly unmotivated, I think that is mainly us not understanding deeply enough what need it serves for the person. Maybe they kill for a sense of control, maybe out of greed, maybe out of a sense of inferiority, maybe...
But almost nobody irl really hurts others just for the sake of it, without getting anything from it. Rather, real evil shows itself in the disregard towards the feelings of others when your desires and theirs come into conflict. There, an actual good person might actively work against their own personal goals in order to protect others.
Take finance for example. Nobody really WANTS to screw people over. I am sure that every single person in the 08 crash would have been happier if it did not happen. But it did, despite some people realizing beforehand that there was a problem. And for some people, seeing that instability was enough to opt out, loosing profits themselves, to not hurt others, for others, it was not.
So basically:
good vs evil = selflessness vs selfishness
law vs chaos = principles vs pragmatism
All companions apart from ironically enough Laezel (who acts in the interest of her people and queen, not her own, she is willing to die to not turn!), Gale (maybe, not sure yet) and Shadowheart act very selfishly.
This can best be seen in Wyll, who yes, like everyone, wants other people not to suffer as long as it comes at no cost to him. But as soon as he has something to gain (Mizoras location), he is perfectly willing to do the most evil acts you could do (torture, imo arguably worse than even murder) without a second thought.
Astarion similarily does not WANT others to be hurt or be enslaved. But I mean, who would?
Would he risk his own freedom and safety so that others can escape that fate though? Would he still do good things if it came at a cost? I am not so sure...
