Seems fairly easy to me. Pay 18 year old boys $10k to get a vasectomy. Watch birth rates plummet. Captialism gives us systematic inequality, we should use it to fix more problems
You control birth rates by controlling FEMALE fertility... not male fertility.
There are mathematical reasons behind this, but for the purposes of simplicity I'll give the lay explanation. ie - A female can only have one (or so) child every 9 months. A single human male can produce one every day. So having a population with only one male, but 100 females, allows for a FAR higher reproduction rate than a population with 100 males, but only one female.
Vasectomy is currently the only permanent sterilization procedure without serious health risks. Barring some strange shift in cultural attitudes where fertile males suddenly become irresistible to every female on earth it should do fine until we find a better way for both genders. Don't let the perfect be the enemy of the good.
In that case... I hope you have some strange shift in cultural attitudes planned for preventing females from being forcibly used by fertile males. I'm not saying we need a perfect method... I'm saying we need a method that acknowledges the realities that many populations around the world live in. Female victimization is a reality in a lot of places on this planet. (To be completely fair... it's a reality even here in the US. Even on the university campus I'm sitting on.)
Rape was the major contributor to population growth in Eastern Kivu back when Nkunda was running rampant. And, to keep everything honest, it still is. (Particularly in Goma). It's not like rape and massacres went away because the Rwandans decided to replace their warlords. The Rwandans still do what Rwandans do I'm sure.
I'm only saying that you ascribe certain properties to the populations you are dealing with. And there are definitely places in the world where your assumptions fail to hold up. But biology ALWAYS holds up.
By the way... I was being kind. Rape is only ONE whole in your plan. There are many. For instance, your plan also assumes women will never simply get horny. Or that they will only "get off" in certain predetermined ways that your plan deems acceptable. Your plan assumes a lot ... and all of it from your own perspective and belief system. If we work within biological limits... we achieve our goals regardless of the local belief system.
That's not the way you control birth rates.
You control birth rates by controlling FEMALE fertility... not male fertility.
There are mathematical reasons behind this, but for the purposes of simplicity I'll give the lay explanation. ie - A female can only have one (or so) child every 9 months. A single human male can produce one every day. So having a population with only one male, but 100 females, allows for a FAR higher reproduction rate than a population with 100 males, but only one female.