You see, I don't think the Forsaken are evil. They aren't responsible for what happened to them. They didn't choose to be undead. They were perfectly happy to remain living humans. Sylvanas didn't seek out her bansheeness. And all other races shun or just tolerate them. So the Forsaken culture is built around the condition forced upon them. Yes, Sylvanas has now taken to, uh, recruiting new members of her race, which most consider very Lich King-like. But how else is she going to expand her ever-decreasing population?
Because the Forsaken are no longer living in the way that all other races are, they cannot value life in the same way. I believe this makes them amoral instead of immoral. They do what they can to survive and even flourish in the hostile world of Azeroth. Of course there are individuals who do despicable things, but you can't judge an entire race on the activities of a few bad eggs.