His dad was the head of Planned Parenthood.

https://billmoyers.com/content/conversation-bill-gates-making-healthier-world-children-future-generations-transcript/

They are huge donators

https://www.gatesfoundation.org/about/committed-grants/2000/10/opp4839

He's always talked about population control.

E. G. His 2010 Ted Talk

The world today has 6.8 billion people. That’s heading up to about nine billion. Now, if we do a really great job on new vaccines, health care, reproductive health services, we could lower that by perhaps ten or fifteen percent.