There was a spoof film made about this very question. I can't quite recall the name, but basically the introduction to the movie explained that humanity had descended into a state of utter stupidity in the future.
As you say, the smart people waited till later in life to have children, and it's a biological truth that the longer you leave it the less fertile you'll be and the less healthy your offspring. Meanwhile the 'intellectually challenged' went on breeding like bunnies, and over the course of many generations the entire human race became utterly stupid.
Obviously that's not going to happen, but it's a disconcerting thought nonetheless!
The other thing I would say is that the desire to procreate is probably very, very low any way, and in truth could really benefit from being lower still, because we've already surpassed 7 billion people on earth, and at the current rate of growth we ARE headed for a major population problem.
And that's not happened, because of the desire to procreate, I don't think. Nature instead gave us a desire to have sex. And that takes care of procreation, condoms permitting.
And so look on the bright side (sarcasm) - there'll always be Catholics!
