As one person said, much of what we see as racist/sexist humor was created by the people it targets (Such as the jews and their very long tradition of self deprecating humor).

It's one thing if Jews or Catholics tell one another self-deprecating jokes, but quite another if someone else tells the same jokes. For example, if *i* make a joke about the Catholic sex abuse scandal, it would mean something quite different from if you told it, even if it were the same exact joke. Humor is very contextual, and the same words can imply vastly different things depending on who is telling the joke.