"it will be backed by a collection of low-volatility assets, such as bank deposits and short-term government securities in currencies from stable and reputable central banks." from the whitepaper: https://libra.org/en-US/white-paper/#the-libra-currency-and-...

It's like one to one copy of the traditional monetary system with speed of transactions improved. Low volatile assets they rely on are not real and therefore not guaranteed to stay low volatile. It may be decentralized technically but not socially or ethically.