It’s not a first amendment issue at all, in the same way that shutting down a phone network isn’t a first amendment issue at all. Any individual can use one of the many other networks available to say what they want to say. The issue is with the network. In this case, with who has ultimate control over the network. Giving an authoritarian foreign adversary the power to monitor all communications in a popular platform and control which communications reach which people is simply unwise.
Regarding evidence, quoting myself from post #87:
A country would quickly cease to exist if it only responded to bad things after they’ve already happened, never taking precautionary measures.
When you know someone is against you, you don’t give them an opening and hope they don’t take it.
And by the way, this goes both ways. It’s not about fear mongering or labeling one country good and one bad. This is just how it is when powerful countries don’t get along. China has already banned US apps, as I would expect them to. They probably ban more than they reasonably need to, but that’s what an authoritarian government gets to do.