Racist humor is always funny, no matter what. Building on that, offensive humor is always funny. I believe no one should be off limits. Blacks, whites, gays, asians, poor people, babies, etc...
Singling out a certain group and saying NO IT'S NOT OKAY is just stupid and doesn't accomplish anything. Censorship just sweeps dust under the rug, rather than confronting it. I'm not defending racism, however, I also think it's stupid to attack someone for being racist.
Like for example, I have no problem walking in with a slice of watermelon and breaking out into Blackface-speech yelling OH LAWDY LAWDY SHO IS DA GOODEST MELLON I EVAH SAW because I know that's not how I truly feel about Black people. Hell, I go to college where white students are the minority, and it doesn't bother me. I just appreciate humor in all its forms.
I think a good summation of my stance would be the classic line of "I'm not racist, I hate everybody." Just because I believe every group of people has some stereotype or traits that can be made fun of.