Ah, I see what you mean. Thanks for explaining.
And, sure, if nobody can seriously express the sentiment that women nag more than men do, or that men are more irresponsible than women, then being able to humorously express the sentiment that all women nag and all men are irresponsible is, as you say, a useful way of averting groupthink. It's not good, but it's better than nothing.
I'm not nearly as confident as you sound that the premise is true, but I agree that the conclusion follows from it.
If people are making a large number of similar jokes, then that's another sort of group think.
As Multiheaded added, "Personal is Political" stuff like gender relations, etc also may belong here.