My concern about Libra is that it suggests that Facebook is trying to control things that have normally been the purview of the government. This is concerning in the long run because Facebook is not run democratically. Any institution performing government-like functions should be at least as accountable as the government itself.
Second of all, it IS accountable to far more than just "rich people". There's many times of democracies... and one way of breaking it down is democracy by vote vs. democracy by exit. The US Government is a democracy by vote. Starbucks is a democracy by exit. You have no control over how Starbucks makes their coffee, but if you don't like it...then you can just go across the street to another coffee shop. That way, Starbucks is extremely accountable to their customers...because if they stop meeting customer demand then they'll go out of business. I'd personally argue Starbucks operates much more efficiently than the US Government (but that's a separate issue). Libra works the same way. Right now, you're forced to use the US Dollar to pay. With Libra, you're under no such compulsion. If you don't like the way Libra is being operated...use some other currency to do your transactions. This will cause less money to be in Libra reserves... resulting in less money to Libra shareholders... and on and on. Therefore, Libra IS democratically accountable.