There's a time and a place for racist jokes. As long as everyone recognizes they aren't genuine. Perhaps the problem here isn't that people think making fun of black people equates you to Hitler, but rather, you're bad at reading a room.
EDIT: relevant personal anecdote
I was eating lunch with a bunch of extremely liberal classmates and we all had a nice fun time sharing jokes. I took a moment to say "Alright, I've got a very offensive racist joke. Everyone ready?"
"How many african americans does it take to change a light bulb? Doesn't matter, the police would just beat the room for being black."
It got a lot of laughs because I took the time to set the joke up properly instead of just coming out of nowhere and going "haha african americans".