it cannot be the world's currency. One of the key foundation stones of government (as well as maintaining your borders, keeping law and order and collecting taxes, etc.) is the ability to control your own currency.
government != the world.
People are the world, and they should care if they want the government and the banks to control their wealth.
Great.
If you want to go be a commie/hippie/libertarian/whatever-you're-having-yourself, off you go and conquer your own territory. There's nothing stopping you.
If you want to change the country you live in according to your personal views -- off you go and change it then. Nothing stopping you doing that either. Just don't expect anyone to listen to you.
If you want to live in an off-grid Mormon commune, put all your wealth into NXT, run FreeBSD and access the internet through a VPN out of Iceland, best of luck with everything.