On the contrary, justice is essential to a good joke, as it releases the tension we feel with our oppressors. It reduces their power over us, and strengthens social ties; that's why (e.g.) making fun of Ivanka Trump's incompetency is funny. Just think of the blank look in her eyes when someone uses a word like "precarity" or "hegemony." Suddenly she looks like a cornered rabbit.

Punching down functions to release the tension of compassion instead--we feel uncomfortable with a group that needs relief from the oppression that we participate in and/or profit from. Such jokes fuel rage and violence.

That's why Dave Chappelle will soon be forgotten--he makes jokes that encourage hatred against Black transgender women. It's embarrassing, and should be. People who are laughing with him now will "forget" they ever did, within a decade.