The Nuremberg Defense of Racist Slurs

I'm sorry, but "I was just joking" is never really a defense when you use racist slurs. And it doesn't make you look like less of an idiot when you use them incorrectly, either:

South Carolina [Republican Jake Knotts] on Thursday called a Republican gubernatorial candidate of Indian descent a "raghead," saying we have one in the White House, we don't need one in the governor's mansion.
...
"If it had been recorded, the public would be able to hear firsthand that my 'raghead' comments about Obama and Haley were intended in jest," Knotts said in his statement. "Bear in mind that this is a freewheeling, anything-goes Internet radio show that is broadcast from a pub. It's like local political version of Saturday Night Live, which is actually where the joke came from."

First, even as bad as SNL has become, I somehow doubt this comparison is worth much. Second, if this is true about SNL originating the joke (which I'm not going to bother to check), it can probably safely be said that they are making fun of the racists, and that is the kind of joke that may be acceptable, if any is.

I'm not really sure why people think "I was just joking" is such a great defense. You're obviously not saying Obama and state Rep. Nikki Haley are literally wearing towels on their heads. And the only people that would think it's "funny" are also racist. So how does this help you?