It's a token i.e. a financial derivative. So Facebook is not giving it's users bank accounts. So there is less regulation e.g. Know Your Customer.
A block chain will make it easier to build trust because (some) third parties can audit it.
A block chain will make it easier to build trust because (some) third parties can audit it.
To replicate that level of success, Facebook must create a mechanism to convert tokens back to cash.
So the tokens are basically just used to get past regulations. Facebook will then gather some hard numbers to show that crime is negligible. Sensible governments will tolerate the tokens because it's replacing physical cash where crimes like tax evasion are rampant.