I don't see why those principles should apply to a foreign country with malign intentions, they aren't a person nor do they represent a populace given that China is authoritarian.

The spying seems secondary to the influence they can wield by pushing certain stories while burying others.

No. The Constitution is not a suicide pact.

Not if it’s a psy op tool of an adversary.

Not in principle. Practically all democratic systems have provisions to defend against subversion of their core principles. Those provisions may be designed to safeguard institutions, processes such as elections and regulate information flow.

It's important to remember that the US concept of "free speech" as an absolute right is very untypical, and that it also has limits due to being narrow in its scope.

Of course, banning a social network due to arbitrary or without reasons would be against democratic principles. But following democratic and legal principles to openly apply laws and procedures designed to safeguard the state - that's not undermining at all, to the contrary!