It is very funny because it is true.
That kind of humor is actually the sort that stirs certain people to action. Sure the joke itself was subpar but that type of humor has always been important to us Americans. Look at the political humor of early on to even now. The humor side is not only making fun of the issue it is pointing a finger at it and screaming "BAD, BAD!!!"
I take it there are no Doonesbury fans in the audience.