What makes vampires "evil" isn't that they're big meanies, but that they prey on humans to survive. It's not that they do it just for funsies (some do, way more than they need, of course).
Since being a DA entails a constant and ever increasing need to consume human blood, that makes them "evil" almost by definition. In a way, they can't help being "evil", from the perspective of humans.
I think the remake makes a good point of puting this conflict into perspective when Ciel explains to Shiki just how hopelessly incompatible humans and TAs are.