I think people tend to misunderstand vampire spawn, and so they don't fully get what's going on with Astarion.
Vampire spawn appeared as they did in life, though their features were hardened and appeared predatory. He doesn't seem to have this too much. Something has changed here because the tadpole. He seems more like a normal person, not hardened or predatory.
Spawn typically believed they were superior to other living or undead creatures, regardless of how powerful a creature actually was.
When it came to a life of adventuring, vampire spawn would seek vengeance on their creators, or penance for their new damnation. If these monsters could overcome their ravenous emotions, they might seek out knowledge, glory, or power. Pride was the true driver of the vampire spawn, since they believed themselves better than others.
He is definitely proud, so that holds true to his spawn nature. He also seems to hold true to the seeking knowledge and power bit. If he feels superior to other living, he wouldn't care one bit about anyone in the game. All that matters to him is his freedom. Everyone else is just a tool or pawn or slave to him. That holds true to a vampire spawn's personality. And, frankly, based on what we know of who he was before his vampirism, he didn't seem too nice then either.
