EDIT: First line on the Georgia Guidestones shows a good reason to do what they are doing. To get the global population under 500 million globally a lot of people need to die off. Fertility being reduced can lead to this as well. Deaths due to vaccines, polluted food, polluted water, and other factors can help get rid of the billions of people that need to go.

FERTILITY: Can be done by reducing fertility. Yet it can also be done by advocating homosexual relationships, and people using VR, Robots, and other ways to achieve sexual gratification. As none of these ways will produce offspring and it should lead to decreased births.