Usually it's considered eminently rude (but not strictly false) to say that the members of your own ingroup are too dumb/biased to discuss a given topic fairly.

Isn't social acceptance of saying rude but not false things exactly what you're arguing in favor of?

In general I do carry a strong presumption against restricting speech. But I have a lot of prior experience that, for "gender difference observations not backed by data", the value of the speech approaches nil in the average case, and is only marginally better on LW, so counterarguments carry a lot more relative weight.