I think that the fundamental issue is that, while reasonable people understand that jokes, even in-group jokes that may potentially exclude someone atypical (for any definition of atypical), do not an unsafe space make... there are still others who would hold up such jokes (which are easy to attack, though not the root cause) and the idea of a "safe space" (which is a good thing), and claim that "this is the problem".

They are wrong. The problem is never jokes.

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.'