If you don't think a given choice fits a given character then don't bloody well pick it. Don't advocate for removing choice that other players may want. Also who the hell are you to mandate what character should or shouldn't say? Why couldn't someone play Astrion on a redemptive path freed from his master he begins to regret his past action and starts down a path of redemption? Or why not play an Astarion as a vindictive asshat that isn't just self centered but vindictive to the living because he was a slave for decades and now that he is free he is turning into yet a different kind of monster? Who the hell are you to dictate other players' approach to their characters? Astarion doesn't have to be played in the way you think he should be played. Sure it is perfectly viable to play as you suggest but i just gave too equally viable reaction based on what we know about psychology of how someone could react to their situation.
Why do so many gamers feel if a player doesn't play the way I play or doesn't like something I like or dislike what I dislike they are doing it wrong? Ever heard of live and let live?
Because....Astarions not my character? He's an NPC with his own thoughts and motives. *shrugs*