It strikes me that you may simply be over thinking this. That you may be placing motivations on things that rarely have any real motivations at all. People have laughed at the absurd, the obvious, the self effacing, and the insulting for as long as we have been human.

So long as we are willing to separate the joke from the reality, what is the harm in humor that is outside the politically correct boundaries that are, by any stretch of the imagination, artificial at best.

I understand how some forms of humour can be hurtful, but we must also ask ourselves, am I hurt by a joke because it was told, or because part of me feels the joke is true about me? If it is the latter, then one must seek to fix what is wrong within oneself that makes one feel that way, if it is the former, we must be willing to step back and remember that we all have a right to express whatever ideas we may have, and that expressing them rather than constantly hiding them is the healthier choice.

I tend to see Comedy as the cathartic system of social interaction. It allows us to give voice to feelings and ideas that may or may not be real, but which may be real to someone, and through their expression and through the expression of them as ludicrous we push them out rather than letting them fester.