I would however be keen to leave the messaging platforms open to avoid disrupting communication too severely. I also see some potential unintended consequences.
Parliaments are sovereign. Facebook violated a lawful summons by pulling a bait and switch:
“McNamee's comments came as an international committee of MPs in Ottawa renewed their summons for Facebook's founder Mark Zuckerberg and company COO Sheryl Sandberg to appear and give evidence before them. Both ignored the first summons, choosing to send company representatives in their place.”
By your definition numerous media outlets could just be shut down entirely. Is that really a good thing? Do we trust the government to decide which information is and is not acceptible for us to consume? I certainly don't.
I personally don't think they should be shut down. (Fines and potentially criminal proceedings, under contempt laws, for Zuckerberg and Sandberg would make more sense.) But they should face some consequences. Keeping all lawful options on the table is a good negotiating strategy.
With respect to metastasisation, that is a concern. But fortunately there isn't a rich history of lawful companies blowing off multiple countries' Parliaments. The one-offness of the situation isn't in countries reacting, but in how complacent they've been with it all.
Perhaps Congress could vote to stop Facebook if they choose, especially since it involves national security, terrorism, acts of war, international threats, etc.
I don't think this counts as a new power. Remember Lavabit[1]? The executive branch forced Lavabit to provide a backdoor to read their customers' email, or pay a $5,000/day fine. They threatened to imprison Levison if he told anyone it was happening, even his lawyer.
Keep in mind, we're talking about the same government that declares concentration camps legal [2], assassinates American citizens without due process [3], wiretaps nearly the entire free world [4], can shut down the entire Internet [5], and recklessly declares a state of national emergency as part of a temper tantrum [6].
1. https://en.wikipedia.org/wiki/Lavabit#Suspension_and_gag_ord... 2. https://en.wikipedia.org/wiki/Korematsu_v._United_States 3. https://en.wikipedia.org/wiki/Anwar_al-Awlaki 4. https://en.wikipedia.org/wiki/Global_surveillance_disclosure... 5. https://en.wikipedia.org/wiki/Internet_kill_switch 6. https://en.wikipedia.org/wiki/National_Emergency_Concerning_...
Loads of business around the world no longer maintain their own websites. The only place you will find their contact information is on their Facebook pages. Sometimes those businesses have added their contact info to Google Maps, or enthusiasts have added it to OpenStreetMap, but so often you have no way of communicating with an establishment without at least visiting its Facebook page.
The same can be said of many bands now. Facebook is how they get the world out about new releases and concert dates. Other sources can lag behind by weeks.