- Many of the problems with the concept of overpopulation start with poor management of resources. Force the residents of 1st world countries to use less with harsher penalties or rewards for being more efficient. Ban Hummers (and similarly inefficient transportation) and create more quickly-biodegradable containers for the waste we generate. We also need to find ways to stigmatize private transportation; too much space is wasted just on roads.
- Find ways to recycle in ways that are useful to the Everyman; I'm sick of seeing grocery bags that say "Hey, now you can suffocate your local wildlife with bags made of 100% RECYCLED PLASTIC!" Let's make houses out of bottles instead of...more bottles. Sure, it'll bend the concept of capitalism right over a chair and go in dry, but you don't win a medal for dying with the most toys. You're still dead, and you're still likely to take down several other people with you. Globally, remove or reeducate the leaders of 3rd world countries to learn how to feed their goddam citizens with what everyone else doesn't use.
- Speaking of dying, let's find ways to waste less space on cemeteries. More mausoleums and crematoriums, imo, and higher costs for burial plots.
- Among the resources that need to be better managed is the territory. Fuck space, you need to get people in extremely good shape before they can handle zero-gravity, let alone whatever long-term psychological damage that may be inflicted as a result of being raised on a floating rock literally in the middle of nowhere. Not to mention that we don't really have the capacity to efficiently look into terraforming otherwise extremely toxic/barren environments in space to accommodate our lives. Our planet has a ton of room and is actually capable of sustaining life, let's try to get along on that before we throw billions of dollars and hundreds of (extremely narrowly qualified) lives away trying to pollute somewhere else, hm?
- I mentioned terraforming. Theoretically, that would be easier to do in otherwise hostile environments on earth. Cloud seeding and demolishing (or at least lowering) mountains would allow deserts to be hydrated and therefore become ariable land again. We could also use more vertical space (ie apartments and condos) and make private housing less popular/affordable. Even more currently speaking, we just need to get into some "wild" sections of the world and pave them over to house the people there. Naturally, this means there will be fewer species to inhabit those areas, but if our OWN population is at risk of populating itself to death, then I'd rather a couple genii of rhinos or birds or something bit the dust than humans.
- Expanding on terraforming: We could build cities underwater. Not necessarily at the bottom of the ocean, but somewhere in the middle - deep enough to take advantage of the massive horizontal fields of space there, but close enough to the surface to keep the costs of communication/supply chains/defense manageable, as well as allowing us to dodge the structural risks of crushing an entire population to death under all that water pressure. Hell, even terraforming islands doesn't sound like a terrible idea considering that 70% of the earth's surface is water.
- As mentioned before, population control. Necessity overrides popularity (as it inevitably does). Enforce a low household maximum (3 children or so?) with harsh penalties for those who violate it. You know, little things like denying citizenship or free education to the extras. Let the parents decide if they want to live with 5 kids, 2 of them living as second-class citizens just because they couldn't be troubled to use a condom. I also approve the concept of finding a way of temporarily sterilizing everyone who requires federal aid (welfare) to stay at or above the poverty line.
- We need to find ways to end wars more quickly. I can't even begin to guess at how many acres are wasted as demilitarized zones, still "active" with land mines and toxic fumes and such. If that means building more lethal weapons and torturing war criminals, so be it. Peace is just the PR-friendly way of saying "we've bombed the other guy into being too weak or too afraid to strike back." We haven't been able to reconcile our civilizations diplomatically for 6 thousand years, why should we keep trying when the stakes are even higher and the figureheads are even more fanatical?
That's my 2c, anyway.