As someone not wanting kids and getting a vasectomy at 27, I personally have multiple reasons why I don't want them. And I know more people like me with many different, personal reasons.

My brother on the other hand has four children, and we have had conversations about this. Although we both want the opposite in life, we came to the agreement that having more than two children is bad for the environment because of overpopulation. He just accepts doing something "wrong", because it makes him happy. And in the end it evens out: some people have multiple children, others have none. All good, if you ask me.