What if people behind Circle or Coinbase become greed? There is no way you can prevent that from happening! People used to say things like this before Mt. Gox stole their money.
Any half sentient being who researched the history of Gox must surely have realised that it was a shit show before the end. No regulation, no communication, no investors, started off with one guy's paypal account, hacks, failures, USD being seized. People were a victim of 'too big to fail' thinking.
Many may not like the way CircleBase operates but there's no denying that they're professionals. The NYSE does not invest in a company that runs off with customer money.