Population collapse is likely not going to come from too many people becoming steralized (I mean what percentages are we talk g about here, there would have to be a massive growth to even make a measurable dent into populations). Typical population collapse in biological systems comes from overpopulation that cannot be sustained by the ecosystem, which results in the sudden collapse. When we talk about the survival of the human race people not having children are likely a net positive, but somehow I get the impression that's not really what your opposition to gender conversion is about