This one's pretty simple: China is a totalitarian regime that is in direct conflict with western constitutional values. So if influence is aimed at democratic foundations, of course it's a bad thing.
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!
[1] https://en.wikipedia.org/wiki/The_Constitution_is_not_a_suic...
The spying seems secondary to the influence they can wield by pushing certain stories while burying others.