You get population booms in the wild but they're generally either sorted out by an equal boom in predators or a starvation from lack of resources which leads to fierce competition and generally less breeding from the stressful situation. There are certain animals that supposedly reduce or cease their mating in a crowded situation for reasons believed to relate to pheromones but beyond that there are rodents like the Lemmings that frequently experience population booms and solve it with a mass suicide (not something I'd recommend for humanity).
I think the real problem of humans isn't so much that we've overpopulated to a point that the planet can't feed us yet, its that we're capable of drawing resources so efficiently and to such an extent that we draw on the resources of other creatures with steady populations and this means they are suddenly overpopulated for what they can take and suffer. By the time we're drawing on enough of the Earth's resources that its really a worry for us, there isn't likely to be much of any other animals left bar those who have learned to rely on us for food to a good extent (rats, pigeons, ibis, domesticated creatures, etc).
When I told him he has three sons out of which at least one will probably have kids, he said it's not the same when it's boys.
(Apparently grandchildren only count if they come specifically from your daughter's uterus.)
Well... I guess a mother is GENERALLY closer to the children (particularly when the kids are younger) and thus will keep them in better contact with her parents than the father's. There are differences, certainly, but I can't imagine I'd get hung up if Evelyn decided to never have kids and I had boys who did.
I think I'd regard the choice to have kids when you want them at least as selfish as not having them when you don't. You don't have kids for the kid's sake, they're not even in existence *LOL*. People could probably only argue for selflessness if they wanted kids but choose not to have them for population or other reasons (inability to provide, etc) or they can have kids but adopt instead. And really, I don't see anything wrong with being a bit selfish and having what you want in life, particularly a big commitment like having and raising a child for something like 18 years.
Like I said, I think they almost feel confronted by someone's choice to not have children as it feels like it somehow collides with their choice to have children. I guess it falls into a lot of things with people going outside normal society's expectations. Women are supposed to (and arguably, generally do) dream of their wedding day and having children, etc. So if you don't believe in marriage or even relationships, they feel like you're bringing down the whole system as they know it to be.
RAGE!!!: overpopulation... We had Dick Smith here in Australia, make a decent push for it in the last election and its all but forgotten now. He desperately tried to explain that if you've got a chair coming into a house every day, it doesn't matter if you work to shift them from the more crowded rooms to the less crowded, the problem is still that you have a chair coming in every day. Yet people still carried on about how Australia has plenty of resources and can take plenty more immigrants, etc... THATS JUST MOVING THE FURNITURE IN THE SAME HOUSE TO A DIFFERENT ROOM!
That was the real problem. It was seen as an argument against immigration and refugees which was a sensitive topic at the time. The white supremest mobs sort of jumped on it and tainted the whole discussion. One great solution is that the selfishness really works. For a little while, we actually had a negative population growth due to low birth-rate in Australia. Most women were working in decent earning jobs, there wasn't a lot of government aid for parents (paid maternity leave, child-care assistance, etc) so many people just couldn't afford it or weren't willing to take the drop in lifestyle to have them. Even then, they had fewer on average. Now all the benefits are in and we have another baby boom.