I think Astarion has poor impulse control, and a blood-thirsty disposition. He could be a murder hobo if he didn't have any inhibiting companions around. I view him as being in a state of arrested development since being in thrall to Cazador, so a lot of his behavior can be childish, in a way that doesn't view the ramifications actions beyond how they immediately gratify.
That goes back to Astarion being a vampire spawn and not a full vampire. In DnD lore, they are bound to their master until their master releases them or is killed by their spawn. Once a spawn is free from their master's chains, they can choose to live in whichever way they want. I even read that in DnD some may choose to live regular lives, not necessarily evil. Not all of them turn to a life of a bloodthirsty monster but live civil lives if they choose. The fun part of DnD is you can create a character and give it whatever back story you want, nothing is said in stone.
