I mean, okay let's break that down.
Young men, okay I'm a man in my late 30s, so throw young out as your argument. Second my wife shares the same thoughts, so, I don't want to speak to her but maybe the gender side isn't as important either.
Childless, well yes, my wife and I are both childless because of the massive problems facing the world today, mostly caused by overpopulation. I'd say being childless is more of a logical conclusion to having these thoughts rather than the other way around. It's also more likely in your assumptions that a married woman with 3 kids would be pro having kids.
I don't know what you thought you were proving, but to me it's very logical why childless people are the people who are in favor of people having less children.