Bitfinex originally denied relation to Tether but it's been proven that was a lie.
The worry is, at some point there could be a "run" on Tether, when the curtains are pulled back, where all the USDT-BTC traders who happen to have USDT holdings and they suddenly become worthless because nobody wants to trade USDT-BTC anymore at 1-1.
As long as "public confidence" in USDT continues, the charade will too