Here is what I HATE about "At Will".... it's yet another idea really only applies against WHITE MALES. Yeah, you might get away with it with a white female, but go fire a black female lesbian and give her no reason, and next thing you know you'll have paperwork served from her attorney with their theory on why you fired her.
On the other hand, I think part of why minorities have higher unemployment rate is because of this very issue. I've heard several of my employers over the past tell me that "once you hire them, you can't get rid of them". So, at will works, but sometimes it works against you too. Then again, that freshly "let go" of white guy comes in, you know you can give him a shot, if you don't like him, you can get rid of him. So I guess it depends on how you look at it.