This is going to sound really wacky, but we crypto junkies are building the infrastructure to get the world through a new Dark Ages.
In the real Dark Ages, after the final fall of the Western Roman Empire, commerce collapsed. A lot of trade was done locally through barter. As a result, long-distance arbitrage was really complicated and frustrating.
And the reason why commerce was all-but confined to local trade was because trust in strangers collapsed too. The kind of trust we take for granted these days, only a bloody fool would have assumed.
Unfortunately, it was also an age where low-trust clusters relaxed into the same old not-so-humane attitude towards "outlanders" (ie, strangers from another locale.) The locals saw them as gulls ripe for the plucking. That's one of the reasons behind the stereotype about "lying, thieving peasants." The other, oddly enough
, was tax resistance...
Back in the real Dark Ages, the only answer to a long-distance "transmission belt" was the Catholic Church. But if a new Dark Ages should befall the world?
Well...what's the Holy Grail of theoretical cryptocurrency? Zero-trust solutions!
In other words, a payment and transfer infrastructure that works to facilitate commerce - including long-distance commerce - in an environment where the guy on the other end of the transaction is one of those "lying, thieving peasants." A fully developed crypto infrastructure - I know we're not there yet, but we're getting there - would mean that you could transact with a "lying, thieving peasant" and have an end result that's essentially the same as if you traded with your cousin who lives a 100m walk from your place.
Okay, okay, but you know what I mean... Granted that a New Dark Ages would imperil the Internet itself: that collapse would render all cryptos nugatory [as well as a helluva lot else that we depend upon now.] But we humans are a resourceful and resilient bunch, so it's not that Pollyannaish to assume that some kind of cobbled-together good-enough Internet would be around.
Now, I know I'm thinking very long term here. But crypto has a more immediate use for more immediate dark scenarios. Back in tha day in Italy, there was an entire factory that the Italian government didn't know existed. [Officially, that is.] Yep, it was "hidden" by a lot of bribe money thrown here and there, and yep - tax dodging was a large part of the "benefit" from the bribes. But, before you guffaw, consider what other reason an entrepreneur would run a "hidden" place of business.
Okay, okay, ye olde drug dealer...but what about a world where (say) a certain kind of light bulb is as illegal as cocaine? Where a tanning salon is seen by the eyes of the law as something like a crack house?
When you're done thinking about it, and you want some off-time, read
The Other Path by Hernando de Soto.
Yeah, I know "It's Can't Happen Here." But on the off chance it does... 
