If/when cryptocurrencies reach the same size as conventional financial systems, they will require all of the same.
Bitcoin is relevant for the US economy and a rogue state tries to have 51% of hashing power? Military and intelligence to the rescue.
Someone is very rich in Bitcoins? Bunker services for offline storage, physical/computer security, etc.
Too many scams with altcoins? Legal enforcement, more bureaucracy, education, etc.
One could say that, somehow, the cryptocurrencies won't require as much of any of that, but I don't see this point being made as often (and not with any realistic estimations).
The 51% scenario: just install more hash power. That would be cheaper and would not risk anyone's life.
Protecting cryptocurrency: there are cryptographic ways to achieve very high security that are free or very inexpensive. Physical encryption keys cost under $100. Combine those with multiple signatures and offline storage in a safe deposit box and you have several physical and cryptographic layers of security for pretty cheap. Services that do those things do not need to be very expensive.
Too many scams? Point taken. We will still need police.
BTW there's a reason I said cryptocurrency and not Bitcoin. Bitcoin is one of the slower cryptocurrencies. Energy spent securing the chain is per block, and its block size limit and other aspects of its design artificially boost its energy per TX. That and in the long term I expect people to find less energy intensive ways to secure block chains.
Bitcoin is relevant for the US economy and a rogue state tries to have 51% of hashing power? Military and intelligence to the rescue.
Someone is very rich in Bitcoins? Bunker services for offline storage, physical/computer security, etc.
Too many scams with altcoins? Legal enforcement, more bureaucracy, education, etc.
One could say that, somehow, the cryptocurrencies won't require as much of any of that, but I don't see this point being made as often (and not with any realistic estimations).