You missed the one that was used for all of human history:
4. Family ties, raise your kids well and establish that they should support you in old age. Bonus: Also gives an incentive to keep strong, healthy families together.
5. When an old person becomes useless, drug him senseless and throw him off a cliff.
Allegedly this was customary among the ancient Sardinians in pre-Roman times. The drug they used on the elderly before killing them induced a sinister grimace, giving root to the expression "sardonic grin":
Facetiousness aside, that's a neat anecdote, but the point stands. Original commentor said there were three options - destitute and possibly homeless old people, after the fact emergency spending, or some sort of pension system. That ignores family/community ties, which is in my opinion a much better solution. You can disagree, but not even presenting it as an option is either being disingenuous or missing a really obvious potential solution.
I guess I tend to group that with the other missing fourth option, "hope everyone saves for retirement". I agree that yes, ideally, people would all find some way to take care of themselves for retirement, whether out of savings, or with family, or some other method. But empirically, in modern societies a lot of elderly end up penniless and alone, so the question is what we do about that.
Downside: using children as your old age insurance policy gives an incentive to have as many children as possible within your means on an already overpopulated planet.
> ...as many children as possible within your means on an already overpopulated planet.
I did some casual research on this - long story short, I think the planet will support at least around 600 billion people fine. You need to speed up nitrogen cycles for food, which we can already do. Energy is the big bottleneck right now, but fusion or whatever comes afterwards will likely make energy almost-free. Further out, molecular engineering and nanotechnology looks incredibly promising...
...anyway, the world isn't really so densely populated. I couldn't find the exact paper while googling, but you could fit all of the world's population in a fairly small state (Maine?) with the same population density as present-day Paris.
More people means more great people, more innovation, more good stuff happening faster. Nitrogen cycles, food, pollution are the bottlenecks. But population 600 billion should be fine and the world will be prosperous if we get there.
I don't want a planet where most of its natural resources are dedicated to maintaining a massive population. I'd much rather have a world where human influence is strong within its own sphere but leaves most ecosystems as pristine as possible.
Greater human population is antithetical to biodiversity and low pollution. That should probably be a greater ethical imperative than maximizing population numbers.
Advocating the past's policies with the future's hoped for or even expected technology is not really what I'd call responsible. At the current time we're not close to having the technology that would let a metropolis the density of Paris feed itself without depending on a comparatively sparsely populated area at least thrice again the size.
That position is a reasonable one and I respect it, but I disagree. Necessity is the mother of invention, and technology is usually developed in response to need. Thus, "don't expand until the technology is there" is a bit of a catch-22: Population growth will drive demand and funding for new ways to solve the challenges that come with it.
Also, population 600 billion doesn't happen overnight - we're almost certainly in good shape for the next 50-100 years, I'd argue the decline in population in some Western countries is a much greater threat to prosperity, health, and happiness than any increase in population could be.
> Necessity is the mother of invention, and technology is usually developed in response to need.
This is some position I respect but disagree with. For one reason: it is pure observation bias.
Those who fail to invent at the face of Necessity take the hit, hunker down and die in anonymity. On the other hand, the ones who prevail have their names written in history as legendary inventors and innovators. Rinse a repeat over a couple thousand years and everybody knows that "Necessity is the mother of invention, and technology is usually developed in response to need".
Malthus is highly misunderstood as having stated that doom in unavoidable. What he actually said is that unconstrained population growth will eventually be forcibly constrained by hard physical and ecologic limits. I'd rather have rational planning or cultural taboos limit the max human population in any given region.
I don't disagree with invention and creativity and a role of a problem in motivating the two -- I can't, really, having ended up writing a couple of odes to it on HN in the past.
However, I prefer my necessities not to involve potential humanitarian catastrophes. The steam engine, the rapid advancement of powered flight technology, and Google were all created in response to a need, but none of these needs were of the "young people will starve and old people will be left desolate if we don't come up with something" variety.
We're not short on need for cheaper energy right now; I don't think we ever were. (More efficient agriculture is a slightly more complex subject due to political reasons.) Maybe someday we will be at a point where we can safely adopt a policy of encouraging lots of children, but right now it seems a little irresponsible.
You missed the one that was used for all of human history:
4. Family ties, raise your kids well and establish that they should support you in old age. Bonus: Also gives an incentive to keep strong, healthy families together.