I don't mean literal monster (although it's technically true), I mean you allow him to become a mass murderer. And by doing this you reassure him his hunger for power is the right thing. You can't just blow up you family and 6000+ innocent people in bloody devilish ritual and stay a good person. As for the Astarion origin - Larian gives the player total freedom and it's the player's "responsibility" to play a consistent character, but if he doesn't want that - he can do otherwise. If you think about it, no player character in this game is consistent, because you can at first do only evil choices and then suddenly only good choices. Larian give you tools, it's up to you how you use them. But NPCs have their own psychology, agenda and personality and can't be 100% controlled by player's wishes.
I don't think he becomes stupid all of the sudden - although maybe the writer could prepare this situation a bit better. At first Astarion is in a uncertain place - it's not clear how he will change (and let's remember he is not a good person from the start). He wants power and when he gets it (again, commiting mass murder as a result of devilish pact with an archdevil)- he corrupts it. This is the consequence of evil choice.
As a post scriptum I will add, that according to D&D rules vampires emotions twist when they become vampires. Love can turn into possessiveness et cetera. But still I think it's less important than the logic of his character arc.
Last edited by Phea; 05/09/23 01:26 PM.