[jacobush]

Fair point.

The US has already "seized" Facebook because it operates under US oversight.

I'm not sure I express myself clearly enough. The US (apparently, de facto) is OK with companies violating all sorts of personal privacy, as long as the US gov has the final say in how the data is used. If a foreign power is doing the same to US citizens, or even non-US citizens, the US is not as OK with it, because it would cede that advantage to some other country.

[puranjay]

But there are countless small and large websites and app that collect private information, perhaps even more egregiously than Facebook because they're not in the limelight.

Why is that not a security risk? If it isn't, what's the minimum number of users you should have before you start becoming a risk?

There have to be some standards and arguments to justify a blanket ban. Just weaving the "national security" wand seems, to me, inconsistent and dictatorial.