The problem, as I see it, is this doesn't really do much to further discussion because there has never been a time in history where there wasn't competing thoughts on similar subjects. For every Simon Legree-esque slave owner there is a John Brown and vice versa. I don't think there can be any doubt as to the position of the vast majority of Northerners about slavery and blacks in general....they didn't care one way or the other just as long as they weren't living next door. It's a sad reality, but that was the reality. Just because many in the North didn't desire slaves of their own didn't mean they were entirely righteous. And of course the same could be said in the opposite direction for good, religious men of the South who also happened to own slaves. The real problem is when either persuasion tries to pigeon hole the other. It just doesn't really work.
Well that's the beauty of it. We get to dig into the complexity instead of just saying "he was a man of his time."