It's easy to mock preppers - that is, people who buy off-grid rural land, a stock of imperishable food, and guns, while honing skills in expectation of the harsh and pre-modern world soon to come - but it's plausible that they're actually providing a public good: redundancy, for the species, against certain awful tail risks.
Let's begin by inventing a distinction: call the ideology "survivalism" and the practice described above "prepping". People often point to creepy far-right tendencies among survivalists (e.g. anti-Semitic conspiracy theories, violent libertarianism, Red Dawn paranoia) and speak as if this were an argument against prepping. No matter how self-interested or politically unsavory the practice supposedly is: competent, geographically spread-out prepping could still help ensure that future generations come to be. "The species", in some sense, and also maybe modern culture.*
(Even on its own terms the ideological critique is shaky: at least one prepper group, the "Doomstead Diner" backed Bernie Sanders in the 2016 US primary; zero-growth anarchism is a prominent tendency in the movement; and anyway if your problem with the people who will survive us after a catastrophe is that their ideology is wrong, then a better response is surely to take up the mantle and go prep yourself, so as to carry real virtue forward into that world.)
Let's make a further distinction between nomad preppers (who prepare e.g. a grab-bag, a boat, and hunting gear) and doomstead preppers (who prepare a remote property including farmland and skills). (People talk about bunkers a lot but it's hard to see how that's a long-term solution.) I'm focussing on the latter, since that's the really sustainable one providing the lion's share of risk mitigation. Shut up and calculate.
Doomstead prepping doesn't necessarily make sense for the individual prepper, since the chances of existential risks appear low and the conditional probability of even a prepper surviving one are also low. But the species can afford to have 0.0001% of the population assuming the worst. We have a word for socially valuable things that are individually impractical: public good. Most reasonable people welcome government supply of such things. Should a suitably resourced world government - of the very sort the survivalists mortally fear! - fund preppers?
How much for a single doomstead? How much for a minimum viable population of them?
This slush piece on American preppers gives a range between $130,000 - $350,000. But property cost is the dominating factor, and is much lower in most of the rest of the world. Assuming we spread out our preppers evenly across the world's arable surface, maximising the risk mitigation, let's guess $150,000 apiece. We would want about 5,000 doomsteads for the species to have a good shot at returning to its present glory,** so that's $750m in total.
What risks could prepping mitigate, and by how much?
What proportion of the total probability mass of existential risks could that $750m cover? This question can be given only the vaguest answer (in fact I'm tempted to give a uniform prior for the following list of risks) and I'm not going to. Instead let's use words and guess the apriori effectiveness of doomstead preppers against known risks:
- Pandemic: high effectiveness.
- Nuclear war: surprisingly high?
- Median-case climate change: high.
- Ecological collapse: low.
- Huge meteorite: low.
- Worst-case climate change: no.
- Gamma-ray burst: no.
- Unfriendly superintelligence: no.
(Where effectiveness is effectiveness at preventing total extinction, and at preserving modern knowledge and values.)
Probability of the risk being realised within a given generation (with the uncertainty of estimating each denoted by the number of question marks afterward):
- Pandemic: medium (??)
- Nuclear war: low (???)
- Median-case climate change: high (??).
- Ecological collapse: low (??)
- Huge meteorite: very low (?)
- Worst-case climate change: low (??).
- Gamma-ray burst: very low (??)
- Unfriendly superintelligence: ? (????)
The answer to the headline question - how good is this strategy, probably? - is hidden in those vague presumed mitigation values and probability assignments. Feel free to plug in your pet values. But assuming that we value the continued existence of the species and its modern mindset at something more than $750m, we might at least withhold our contempt for them.
Hey how do I join your apocalypse cult?
My claim is not that doomsteading is anything like an optimal allocation of resources: for instance, $150,000 is enough to supply an entire developing-world town with malaria nets and anti-helminthics, saving hundreds or improving thousands of lives; and the uncontacted tribes of the world already give us about as much species insurance as we can expect against these events.*** Just that in one sense it is less irrational than it is commonly said to be.
* Moreover, preppers provide this insurance good in a revenue-neutral, decentralised way immune from cuts. (Research on the actual relative stability of private prepping expenditure is understandably not found.)
Certainly this payment structure means that only middle-class paranoid people can afford to be preppers - and certainly the fringe nature of the activity means minorities are less likely, just for statistical reasons as well as because of class and any putative inherent racism in the movement. ⏎
** I've never found a clear answer to what number of people constitutes the minimum viable human population. But the entire current world population could well be based off c.5000 breeding pairs, so that gives you an idea. ⏎
*** Though not cultural insurance. It would be a pain in the arse to wait for modernity - integer economic growth rates, science, liberalism, feminism - to recur, over the millenia.