Depends how far back you go. Child mortality rates have been declining. It used to be that death of children was fairly common, and there was no government support to pay for large families. The improvement of health care and the increase in government assistance to raise large families have helped.
AZ, On a rational, intellectual level I agree with you. However, clearly on some level we have to suspend rational thought and have bitachon. Based on the tuition crisis, people rationally should have smaller families. People should go to work right away instead of learn in kollel. I give a bracha to anyone who marries close in age as well (al tehi birchas hedyot…). But I would be foolish to call those who do not destroyers of the world. It could be bashert that some women never get married. Rationally speaking, we should abort 2 out of every 100 female fetuses to keep the ratio intact. Would you advocate that as well, or would you say “bitachon”?