It's not a "mathematical" solution. The maths are cryptographic hashes and consensus protocols, means to some end - exchanging value. You're proposing that it'

It's not a "mathematical" solution. The maths are cryptographic hashes and consensus protocols, means to some end - exchanging value. You're proposing that it's a technological solution to a societal problem. These only last as long as a particular regulatory body / regime allows them to. Mining. It has long been infeasible for anyone without prior capital and investment. Ban that - you can easily get a lead through the electricity bill - viola. Private key custody. Even technologically-inclined individuals mess it up from time to time. Hence the proliferation of centralised services to keep the keys ("wallets") for you. Block the exchange. QED.