This article is far from perfect (I disagree that the motive for keeping slaves was getting stronger from 1820-1850) but it is a good place from which to start a discussion.
Urban Warming and Racial Climate Change
Walter Russell Mead
In one of those lapses of news judgment that with regrettable frequency make mainstream journalists resemble characters in Scoop, the media herd that gathered in Wisconsin to chronicle the great Democratic triumph in the state senate elections has gone back to the coasts — and missed what could grow into a much more consequential story than the failure of organized labor’s second attempt to punish the Wisconsin GOP: the outbreak of racial hate violence at the Wisconsin State Fair. A story that involved Scott Walker getting his just deserts, even if it didn’t quite work out that way, was infinitely more interesting to our national press than a deeply disturbing gaze into the fragile nature of our social peace.
Another good article: http://www.conservativecommune.com/2011/08/the-left-that-cried-tea-party/
Some suggest that we should ignore this nonsense. I suggest that we should highlight it, answer it, and make the left own it. If a meme like this is unchallenged and left to fester within a community, it becomes conventional wisdom to them. If it is highlighted and challenged publicly, we force them to answer their charges—and the media must ask questions of those who are making blanket statements without facts to back them up.