There are several things going on here -- Today, banking controls the monetary supply through creation of new dollars to be loaned. Being fully backed has less meaning in a continuously inflating fiat currency world. Being backed by gold, by computation, by proof-of-stake -- these are all much stronger measures than JP Morgan Chase's core banking database.

Libra is control over monetary flows. Offend zuck, watch your public key added to the block list. Watch the balance drained from your account as the producers use 'admin' transaction powers to remove funds. Maybe the ledger maintainers simply block your transactions from being committed.

And then we have currency controls in places other than the US, like India and China. Suddenly 'stablecoin's are more useful than bank account backed dollar holdings (outside the US). This is a power grab for the future currency of developing nations. The endgame is control of planet Earth's M1 currency supply.