I don't know if it's FUD or a valid concern... but today all the talk is of USDT (Tether) losing its peg to the USD and crashing Bitfinex.
It could just be an irrational panic... but it illustrates the dangers of relying on a centralized third party. The truth is that even if USDT is fully backed by USD in a bank account, it would only take a couple of banks deciding to no longer work with Bitfinex for USDT to become unconvertible and unredeemable.