The protocol may be open, but the permissioning participants are (as of writing) large multinational corporations. If a country tells them that they have credible reasons to believe Libra is being used for money laundering, tax evasion, or gasp funding terrorism, they will be more than happy to close those channels down.
From the article, we also have this quote (h/t 'Lucadg)
> At the core, we believe that a network that helps move more cash transactions — where a lot of illicit activities happen — to a digital network that features regulated on and off ramps with proper know-your-customer (KYC) practices, combined with the ability for law enforcement and regulators to conduct their own analysis of on-chain activity, will be a big opportunity to increase the efficacy of financial crimes monitoring and enforcement.
Considering that most of those have countries have trouble enforcing the most basic tax laws, I'd like to see them try banning digital money that can be transferred over encrypted channels.