I don't know how many of all y'all have spent much time in The Deep South ("American by birth, Southern by the grace of God, retarded by the heat and humidity."), but white people love to see other white people being treated poorly by blacks, especially if those "other people" are northerners. It's a sort of "We tried to tell you so!" teachable moment regarding what happens when you give "those people" "a say".
The punch line turns out is that whoever orchestrated this bombing at the NAACP is right. And because stereotypes exist for a reason, it allows the Romney folks to say, "Well, sure, this guy may well indeed be the president and all, for the most part. But he's still black, which means we can pretty much say anything we want about him."