In reality, everyone isn't going to go vegan overnight. Nor are they all going to stop having children overnight. The difference is, if everyone DID stop having children overnight but carried on with the same lifestyle they have now, we'd still be doomed - the population wouldn't reduce itself fast enough to avoid the 2-3 year tipping point deadline that's been postulated. By contrast, if everyone went vegan overnight, then the environmental impact would be drastically reduced several-fold overnight. Personally, I prefer both options. I haven't had kids and I'm vegan (and I don't drive or fly, etc.) It baffles me why people always seem to make excuses for not doing the right thing by putting forward the argument that it's better to do some other thing instead. We should be doing every-fucking-thing we can to change our course, not arguing about which single option is more preferable. Personally, my reason for not eating animals or their secretions is because I have no right to exploit or abuse someone just because they're a different species, any more than I have a right to exploit or abuse someone because they're a different race or gender. Veganism is an animal rights issue. I'm merely pointing out that a side effect of increased justice and respect for other sentient beings might just help humans survive, too.