I haven't looked at ripple in awhile, but I thought the idea was that if Alice agrees that she can float Bob $5 and Bob agrees that he can float Charles $5 then

I haven't looked at ripple in awhile, but I thought the idea was that if Alice agrees that she can float Bob $5 and Bob agrees that he can float Charles $5 then as long as you trust Alice with a $5 debt, you can trust Charles with a $5 debt, even though you don't know Charles. And in practice it's usually that Alice and Bob are banks, and Charles is just a customer of Bob's bank. So, Bob can freeze Charles' money. What you're talking about sounds more like EOS, Cardano, Ethereum Proof of Stake, etc.