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.
Likewise, when corporations become too powerful and monopolistic, they are technically "democracies by exit." But, much like some countries, they are not democratic in the important sense.
When such companies exercise too much power, most ordinary people do not have any control over the forces that most significantly impact their lives. And it is this sort of distributed control which makes a system democratic or undemocratic.
I have no idea what you're trying to say with this. Just because you don't need an exit visa to leave doesn't mean other countries will just take you in.... That's why you have refugee crises.
You're going off on a completely different tangent. When corporations become too powerful and monopolistic then it's the government's job to break them up and preserve competition.
We're specifically talking about Libra right now. Libra will have competition with the US Dollar. Unless you're suggesting Libra will become so powerful as to replace the US Dollar...then your point is completely invalid. Additionally, if Libra is extremely successful, you can almost certainly bet that other companies will come out with their own digital currency.