This gets interesting, especially with Dave Chapelle, but professional comedians like Dave and Seinfeld etc. have one very specific attribute that allows them to punch up, sideways and even down – everyone always knows they're joking (sometimes even when they're not). And comedians have no power of their own, so they can speak truth to power as much as they want.

The problem is only when someone with power punches down, unlike a professional comedian (who has no power over the group s/he's punching at). That's fine, we can all laugh at ourselves.

There's also a problem with punching down when you're not a professional comedian, because now nobody knows you're joking. If you try this, you'll sound racist/classist/sexist/elitist.

The rules about comedy don't apply to professional comedians, because you know if they break them they're still trying to funny. Just like if a beginner plays a bad note on a piano, it's a novice mistake, but if a master does it it's dissonance that shakes your soul.