You're right, the problem is never jokes: it's the social power behind the joke. If I am upset, and I say "I'm so mad, I'm going to kill you!" in a joking manner, that's one thing. If I say "I'm so mad, I'm going to kill you!" while brandishing a handgun, well, that's an entirely different manner. I'm not sure why you're bringing up jokes, neither page I linked to contains information about jokes.

The point of safe spaces is not to protect people from jokes. The point of safe spaces is that a place exists where, for example, you don't need to explain for the Nth time how $SITUATION is or is not marginalizing against $GROUP, and feel safe that no members of $OPPRESSIVE_GROUP will show up and derail/invade/disrupt/cause harm to the group.

To answer via your original question, it is 'safety in homogeneity.'