well, Tannywheeler, I would not rule out various 'adjustments' applied to men...but the truth is, it would be more complicated (chancey surgery), expensive and less efficacious. Women are the 'bottleneck',that is, one man can provide sperm to fertilize many, but a woman can only produce progeny at a certain rate. (Future space colonies will need MANY extra women, probably). To be effecient, contraception MUST be applied to women, and the techniques are already well understood....if it is also applied to men in some way, that could be a bonus.