A percent of the population (around 10 or so last I checked) being homosexual is hardly going to cause reproduction to stop all together and the end of the species. And besides they're going to be homosexual and "defy nature" weather they are allowed to be married or not so your point is pretty much moot. And if they are allowed to be married why can't they just adopt children? There are plenty of hetero couples that can't have children and yet get married anyway and then go that route, however by your rational they shouldn't be allowed to be married because they can't reproduce.