If all but ten of the original one hundred men were sterilized, and we asked for the same results, those ten man could still impregnate all one hundred women. If we then sterilized 90% of the male population before it reached maturity, the remaining 10% could still continue the experiment and impregnate every girl.
But if all but 10% of women were sterilized in any given generation and none of the men were sterilized, every generation would see 90% less pregnancies.
Long story short: Women make babies.
That's important to remember, because the biggest, and perhaps the only, challenge facing humanity is overpopulation. Challenges emerging from peak oil, global warming, and war are compounded by human population to the degree that radical responses to these issues are practically nullified unless humans depopulate planet earth. Moreover, we can greatly mitigate most of the dangers these issues pose if we radically depopulate.
The best thing about depopulation is that humanity loses nothing. No culture, nation, or language is sacrificed. Humanity is not any safer or progressing any faster by having over six billion people instead of under three billion people living on the earth. In fact, the opposite is the case. We might have twice as good a chance of giving birth to a genius, but with overpopulation we don't have the resources to properly educate every child, so that potential is wasted. Not only that, it is a lot more efficient to have a billion fully educated humans, and no others whose existences are limited to surviving, than over a billion educated with 6 billion more that tax resources.
Sterilizing women is the key to depopulation, and that may mean it is the key to humanity's harmonious survival. Incentives to depopulate in the form of cash, education, jobs, tax relief, free tubal ligation, and easy adoption should be targeted at women. Casting women who sacrifice having their own children in a heroic light should be an essential of advertising world over. Sex education must provide free contraception and impress the importance of women waiting to have children and having only one child and no more than two if they are determined to have their own. Incentives can be scaled to decrease with one and two children, with tax social penalties for women that have three or more. Social services must reward depopulation and cease to support overpopulation.
Legitimate incentives will also increase women's social power, which will engender more balance and fairness in our societies.
This idea needs to get more popular and current, and fast. The more the necessity of depopulating the earth comes into focus, the sooner we can inject these ideas into the machineries of our political, economic, and even religious institutions. If we do not act in haste, it may even get to the point where we need to apply the kind of pressure that considers women who have children at an early age and/or three or more children to be selfish.
Without this concerted effort, as unpopular as it may be, we are left with a much grimmer and darker alternative. Either way, humans are going to depopulate this planet. We can do it consciously, peacefully, heroically, and proactively, or the planetary circumstances will do it for us instinctually, violently, frighteningly, and passively.