"Buy why?" If you have proof of passport, you have proof of identity (at least up to the difficulty of obtaining a counterfeit passport - pretty expensive). If

"Buy why?" If you have proof of passport, you have proof of identity (at least up to the difficulty of obtaining a counterfeit passport - pretty expensive). If you have proof of identity, you have secure private online voting. You also have solved the astroturfing bot problems, and multiple-accounts problems on most communication platforms. Want to get into cryptocurrency-specific applications? If you used that proof-of-passport design and issued an inflationary currency around it such that inflation was issued one-coin-per-passport, then you have a currency that auto-taxes the rich and auto-distributes a UBI (parameterized however you like). Could be governed via online voting. Would need to have considerable penalties (or bounties) to those who are found with fake passports though. This currency could be quickly substituted with effectively no usable difference to most people for anything currently purchasable with Bitcoin/Ethereum/etc. It could also be used as a decentralized asset registration system for non-cash assets. If enough people simply held and used this currency as opposed to other crypto or USD/etc, and enough started requiring buyers/sellers to use it (for political reasons at first, then later practical reasons) then its price would quickly stabilize and make it a reserve currency, and there's not much any other party could do to stop it. Participation in the economy could then effectively require use of this currency, which means effectively registering your assets and your accounts under a single identity and exposing those assets to automatic taxation in their effective value due to inflation. It is simply built into the system at that point. Though this inflation relationship could be set to be a net benefit users up to a net worth of e.g. 2 million USD equivalent. This also opens the doors for automated anonymous auditing of assets, anonymous proof-of-ownership, etc. Enter "but we could do this already without cryptocurrencies!" - sure, probably. But now you can do it without centralized control of the system by anyone.