I'm going to flat out say first that Dunham is a hack, and admittedly awful. However, he's just doing the type of humor that I personally find funny, that is done better by better comedians. Dunham's stuff is probably tame to the comedians I like, i.e. Jim Norton, Louis CK, Stephen Lynch, and Bob Saget. I know you're going to assault my character, but whatever... they're hysterical.
Comedy is a form of escapism. If I laugh at a joke about sucking dick for crack, or a song by Stephen Lynch about the Special Olympics, for example, that's my prerogative, and I have every right to laugh about it. It's lowbrow, but I honestly don't care. And XFear complaining about Dunham doing ****** jokes is what is wrong with society. So what? He's just trying to get people to laugh. Denis Leary actually just came under a lot of controversy where a bunch of parents with Autistic kids got upset because he did an Autism joke. So what? His job as a comedian is to make people laugh, and if it goes to shock value, then so be it.