Women stop having sex so that men will stop fighting wars. And, unusually, sex strikes are proposed all the time - whether or not there is any follow through is an entirely different story. The article gives a few examples, citing places like Kenya and Colombia (where women stopped having sex to get the government to pave a road connecting them to the city) as a few locations where this has happened. Another great example is Belgium.
Now, relating this back to the Reader, we've been talking about the right to sex, age of consent laws and the generation gap between Michael and Hanna. What right does Hanna have to sex, does Michael have to sex, and do the men fighting for their nation have to sex? A movement purely designed to stop a war through withholding sex highlights the societal value of sex, not only to men, but also to women.
Age of consent laws can, arguably, be put in place to protect innocence and inhibit bad decision making. But, in cases with Michael and Hanna, one can argue that Michael was mature enough to make his own choice and pursue his right to have sex with whoever he wants. What place does the government have in regulating sex? Or, even more interestingly, how can sex - more specifically, a sex strike - affect a government or militia, and its actions? These women are exercising their right to have sex by not having it, hoping it'll change the world - or at least end a war.