I think you're misunderstanding me. Obviously Astarion is enraged if you sideline him from his own well-earned revenge and make his decisions for him. That route doesn't just deny him agency, it denies him closure.
I'm saying he's conflicted about what he has to do to complete the ritual, and he's shoving down that conflict and insisting everything's fine until that makes it fine... as Astarion generally does.
Astarion badly wants the ritual. That's, like... super obvious. It's everything he's ever craved. But he doesn't want to have to kill his siblings for it, nor his victims, and he tries unsuccessfully to convince himself he does/that they don't matter. Both banter and devnotes support this (off the top of my head, if you confront him about lying to his siblings that he plans on killing them, he does privately think that's going too far), his breakdown at encountering his old conquests aside.
