I've been an advocate of population reduction since I was a kid and learned about overpopulation, and in ways that overpopulation and the stripping of the environment has lead to the cycyle of African starvation. Too many trees get cut down for firewood, so fertile topsoil gets washed away when it does rain, leaving poor quality soils to grow crops on, crop yields aren't high enough to support the population, so people starve.
I don't believe humans have any moral 'right' to reproduce. I don't believe we are any 'better' than the other species that inhabit this planet with us. We may be more aware of ourselves, and able to reason, but why does that make us better? I don't see it.
1) I agree, get rid of the kid tax credit for any children biological children over 1. Allow additional tax credits for adopted children. As people have less kids, there will be less kids to adopt, and over time, the multiple child tax credit will fade.
2) Give couple the right to have 1.5 kids. Obviously you can't have two or more kids if you only have the credits to have 1.5. So what's to be done? Kid credits get traded and bartered. You want two kids? You have to purchase someone elses 0.5 kid credit. You don't want any kids? Well then, you have 1.5 credits to sell to others. I've read this idea before, and I think it'sa great idea! And the 1.5 credits is for the couple. So each individual would only have the right to 0.75 of a kid. So lets say you get married, have a kid with your spouse, and don't use or sell your remaining 0.5 kid credit. You get divorced and remarried, your new spouse has the right to 0.75 of a kid and you have the right to 0.25 of a kid (if you and your ex decided to fairly split the credit between the both of you instead of selling it as part of the divroce or give it to one of the parties). So after your second marriage and breeding stint you wouldn't be allowed to have anymore kids. And neither would your new spouse since he/she used up all of their 0.75 kid credit.
3) How to control people breeding? Well, we could always do like culture in the novel "The Sea of Glass" and take the unlawful extra children away fromthe parents, execute one of the parents as punishment, send the extra kid to a forced labor camp, and if they are just a baby, turn them into hamburgers. No I don't advocate that at all. It was a disturbing book. But I would totally support a forced birth control policy for both women and men. Depo shots for women, and some other reverisible form of BC for men. And when you get married and want to have a child you haveto go through a class and get a certificate showing that you are ready to be a parent and stop BC. Then once you have your kid you can choose sterilization or more BC until you purchase another kid credit.