The birth rate of 1.5 children per women in Canada for example is unsustainable. Having it less than 2.0 means a lot of people are not pulling their weight in society. While there are other factors, not having children is immoral. For one, who will take care of you once you are no longer active? Our system relies on the next generation tax to pay services to elderly.

If the system requires forcing people to give birth, it's the system that is immoral.

That's what selfish people tend to say about moral principles they don't want to follow :P.