Cryptocurrency has a pretty big problem: "dollars, but without US Government oversight" is exactly what money launderers and other financial criminals want to have. The closer any cryptocurrency gets to being this, the more illegal activity it will facilitate and the more risk the project takes on of getting the entire operation seized and the principals arrested and extradited to the US (see also: Liberty Reserve).
You could equally say "Speech, but without US government oversight, is exactly what the pedophiles and terrorists want to have".
I'm honestly not even worried that Facebook is going to flout AML laws. I'm more worried that they'll use the fact that they're using newfangled technology and the political and economic weight of their crypto consortium to get favorable legislation passed. And then, because of said crypto features, we'll end up undermining laws that fight money laundering and other financial crimes.