And how do you propose to achieve this? How do you reduce population without trampling on an individual rights? Even with China's 1 child policy, it has only managed to slow population growth. The countries population has grown by about one billion since the policy was enacted.
Certainly there are benefit's to a lower global population, but the downside is what the world would need to do in order to reduce the population.
For the US?
1.) Bring all US military home from EU once we're out of Afghanistan. Those still in military lock down southern border. Anyone attempting to cross that does so in an area where detention is not guaranteed, and won't take warnings to leave, is destroyed. The continuation of illegal invasion would be over. Mexicans (and those that travel through Mexico to illegaly come here) would be Mexico's problem, not ours. If Fox doesn't like this, that's even better: He can actually take steps to fix the problem rather than foster it.
2.) Since we'll never get rid of SS or Medicare, rather, we'll eventually go to UHC, enact tiered UHC: Basic, Plus, Premium. Everyone in the US gets Basic, if people want more consideration than what Basic will provide, they can pay themselves for additional level of care. You can't have an adult contribute nothing to Fed taxes, and expect $2M in care. Don't want to not get high $$$ care? Net contribute then.
3.) Since we now don't have 1/2 of Mexico + other countries illegally F'ing up our country, plus we have people getting at least Basic medical care, we can now chop spending on the multitude of Fed. Those states/counties that want extra that was chopped, no problem. They can pay for it themselves. The people in those states/counties will have exponetially more voting control of what they want/don't want than the insanity that is Fed spending.
4.) Since Everyone now is a US citizen, and has Basic healthcare, and we don't have f*cktons of illegals, we can now work. On Unemployment? That sucks! On Unemployment past 30 weeks (that's more than 1/2 year)? Bummer for you. Report to your local government designated place x times a week to do whatever the F they want you to do. Look at that...less people on the Unemployment rolls (if they're forced to work, they'll be MUCH more apt to at least get paid better money for having to do it). Those that aren't on UE and don't want to work? Either they can afford to or they're going to be some really poor F's.
5.) Now that we've fixed the major F up problems in the country, or, at least some of them, we institute a tax credit program for women over 18, giving them credit to not have any kids. (assuming 1 kid per pregnancy) Have one successful pregnancy, less credit. Have two successful pregancies, no credit. Have three, tax penalty. Have four, more tax penalty. Have more than two pregnancies and can't afford the tax penalty without government assistance? Forced sterilization to solve your lack of control problem. Men or women wanting free sterilization would get it at any time.
Sounds very reasonable to me.
Thing is, something like this will eventually happen. Might take 200 years, 300 years, all very short periods of time, but, it
will happen. "The world being able to support <absurd number> Billions of people" does not mean the World can actually support those number of people in the lifestyle they'll expect to be supported in...it means we can
sustain life at that population level.
Get something like my #5 implemented now before the 15 Billion people in the future world eat up every resource on the Earth that took millions/billions of years to get there, and will take millions/billions of years to reform. Social whining now, or, social anarchy later. Pick one.