The thing with PoS is that when you control >51%, you better not mess up, or you will soon own >51% of nothing.

With PoS the people who have the most control also have the most incentive to keep the value up for everyone involved.

PoW is not like that, since the one who has the most computational power doesn't necessarily own the most coins.

Multiple governments in the world, and multiple means of payment and value stores seems like the most robust to me.