If they were really selfish, then they'd stop being parents. It's not selfish to say that something you're going through is hard or sucks if you're still putting in the work.
The answer is not for there to be less people--less youth and vitality in the world--or to deny anyone the right to have children (within limits. You can't just be plopping out 5 kids if you're a broke fuckwit).
