One way to decrease population is to do exactly what the status quo is promoting right now. Become a vegan, change your gender it's awesome, fight for women's rights so they can be happier in an office all day and not have time to give birth and raise children, feminize men  .

It's already happening. Populations are being weeded out because there are too many of us. Antibiotic-resistant bacteria? Vaccines? I don't buy it.

This is why the Virternity project's vision is so important.

https://en.wikipedia.org/wiki/Virternity