> So why should we trust the least trustworthy among us any more than the new kid on the block?
But you seem to be forgetting the golden rule: whoever has the gold makes the rules.
Governments only exist to raise revenue -- and then spend it¹. Therefore it's easy to see that they, above all others, have a vested (literally) interest in supporting the value of the currency they, and therefore by association: we, use for those transactions.
You may be suspicious of them, but where money is concerned they are extremely motivated to retain the confidence of the international markets and thus the value of the currency. So if nothing else can, that at least will keep them on the financial straight and narrow.
 There's also a small matter of creating laws. But that's largely irrelevant to this conversation - and anyway, we pretty much have all the laws we need. We just need to implement them better.