I agree that the words politically correct have nothing to do with politics or correctness. They are slurs. Uncivil utterances. Everyone knows what the boundaries are, so that any sentence that begins with, “This may not be politically correct but,” signals to the listener that the speaker or writer knows that a line of civility is about to be crossed. Why someone feels compelled to cross it, and face it Bill Maher can’t let it alone for one show . . . well, maybe one . . . it points to the fact that someone needs this joke to burn off the stress.
When I transitioned, I was amazed at who was okay with it and who was not. (This was back in the 1970s so it might be different now.) Some of the biggest liberals (politically correct?) were rejecting and hostile, while some of the very most devout fundamentalists, who I was sure would stone me, embraced my new (to them) identity. The reason I bring this point up is that it cuts across liberal/conservative/whatever lines.
But as long as there is stress, there will be off-color jokes. To heck with who is the butt of the so long as the majority group can laugh away their discomfort.