It's not really all that surprising, is it? Of course Sora isn't going to fully accept the idea of creatures of darkness being constant companions. Not that Vanitas really has a choice on the matter. They had been created due to his separation from Ventus. As long as Vanitas exists, they exist. If they exist, Vanitas can continue to exist. They are, after all, pieces of himself. In that sense, to reject them is to also kind of reject Vanitas himself.

That being said, Vanitas doesn't really care about being a better person nor does he really know how to be. Darkness and negativity are all he's ever really known.

Which is why this whole situation is weird. It requires him to be somewhat friendly and actually communicate with people. He has to try to not completely alienate himself, though he's likely going to do that in the end anyway. Still, Sora's inquiry isn't what he expects. No one actually asks about these things.

"Yeah?" He answers, slowly. "It gets harder the further away they are, but they're still a part of me. When they're cut down I know it instantly. I figure that's how we'll know if they find someone. Or it will come back."

Though the chances are higher that the Unversed will be attacked. Monsters are monsters, after all.