Many things in life do not have logical answers. Two variables in an equation such as this, pro-life and complaining of overpopulation, may actually not be related with people who do the two. Their belief in pro-life may come from a personal experience that effected them deeply, and complaining may also be a course of action this person has taken since childhood. He may say it and not take a second thought about it. And it may not effect him emotionally.