Trains got bootstrapped with speculation... but they were clearly useful before the speculation.
Same for the Internet.
As you admit yourself, cryptocurrencies are a solution looking for a problem. They do nothing, they provide nothing, they're just—"valuable". It's a scam, thousands of people will lose money, and you will have done your part to help those people lose money.
Now you're breaking another of the site guidelines too: "Please respond to the strongest plausible interpretation of what someone says, not a weaker one that's easier to criticize."
Could you please stop now? You're a fine HN commenter otherwise. It's fine to be skeptical about cryptocurrencies, as many HN users are—but it's not fine to do flamewars or break the site rules.
Solutions looking for a problem are OK and are a healthy part of the economy.
In countries that have problems with their fiat currency, non government controlled currencies are quite useful. Especially as crypto cannot be confiscated.
Or, if you're a complete and utter pessimist: When there are too many solutions looking for a problem, it could also mean that there is too much money in the wrong hands.
Same for the Internet.
As you admit yourself, cryptocurrencies are a solution looking for a problem. They do nothing, they provide nothing, they're just—"valuable". It's a scam, thousands of people will lose money, and you will have done your part to help those people lose money.