I rewatched Sunday's episode again, and I think that that blackface stunt pointed to something powerful (if unoriginal) about racism--how it reflects on its bearers. Roger looked ridiculous. In part this was because he is ridiculous, blackface aside. But it's also because blackface--seen in full color like that--looks ridiculous. I may be off on this, but I've just never thought blackface was funny--not just offensive, unfunny. I have no idea why people, decide to show up to parties in the stuff. And yet they do.
I think it's a waste of energy getting offended about this sort of thing--mostly because it says so much more about the person in black-face, than anyone else. It's like the Confederate flag, and "heritage not hate." Why get upset? These people are walking around with signs that say, "I'm ignorant of the basic facts of American history, and I'm proud of this." Why be angry at that? It's on them.