What would happen. . . if suddenly . . . men could menstruate and women could not?
The answer is clear - menstruation would become an enviable, boast-worthy, masculine event.
Men would brag about how long and how much.
Boys would mark the onset of menses, that longed for proof of manhood, with religious ritual and stag parties. . .
Military men, right-winged politicians, and religious fundamentalists would cite menstruation ("men-struation") as proof that only men could serve in the army ("you have to give blood to take blood"), occupy political office ("can women be aggressive without that steadfast cycle governed by the planet Mars?"), be priests and ministers ("how could a woman give her blood for our sins?"), or rabbis ("without the monthly loss of impurities, women remain unclean").
Adapted from Gloria Steinem, "If Men Could Menstruate," Ms. (October 1978), p. 110