The origin of physical currency -- coins -- happened 2000 years after money was invented. Coins were invented as a way to provision armies.
It worked like this: soldiers were paid in coins. Taxes were required to be paid only with the new coins. The only way to get the coins, to pay your taxes with, was to sell supplies to soldiers who had coins. Armies supplied, check.
Facebook has an opportunity to force its coin into use by a similar stratagem: offer advertisers a discount (at first!) if paid in Libra. Advertisers can only get Libra from Facebook account holders. Advertisers have to sell at a discount, for Libra, to get enough Libra, but they get it back in the advertising discount. If buyers want these discounts, they need to get Libra from Facebook.
Soon, Facebook controls the economy of the world.
It was recently explained to me that Facebook only wishes they could be as evil as Google, but they were way behind. (Google passed Microsoft sometime back.) This could leapfrog Facebook far beyond Google's dreams.
Are we in for Dystopia? I can't see how not, unless they fuck up so it's both too hard to use and too easy to get ripped off.