Ya, that's distributed adversarial consensus. Decentralized currencies are an excellent instance of such conditions. They really are a useful and interesting application. That doesn't mean they deserve all this hype in the form of investment from the average person, but if they weren't so hyped, they'd have a serious use-case as a world reserve currency and they'd make a very nice international settlement layer. Because all of the countries in the world would know that the currency was politically neutral. I think that's a pretty sweet/useful property to have.
There are definitely a few other cases where adversarial consensus problems exist too. I think decentralized prediction markets are a pretty great application of smart contracts, for instance. But yes, a lot of these things are way way over-hyped and being pushed for things way beyond their useful scope.