Not commenting on the morality of it. But consider the fact that hes been a vampire spawn for a good while now. And he hasent gotten the best of treatments during this time. This warps your sense of self. Your selfworth. How you value others. How you vieuw the world and the people in it. Basicly....it warps everything of your psyche.
Regardless of the how or why he became one in the first place (dident run into that part of his backstory yet. But generally speaking you dont do it for fun...) the anwser could also be something simple. Maybe hes just a little bit of a dick?
I dont know. Think only the devs can anwser this one with a complete 100% truthfull anwser. Think we can only speculate.