It can be construed either way.

If you want kids, its selfish to bring the other party into existence. Life isn't all great, and you don't have a choice in whether or not you're born.

If you don't want kids, its selfish because you are not supporting the society (other party) that supports your existence. If we don't have kids above the replacement rate, society doesn't continue. If you are fine with that great, but its hypocritical if you plan to continue to benefit from society in your own life.