It is that infringement of the rights of others which is the very issue at hand here! The government undertook actions which caused people to be unable to express their opinions.
That the government was "just expressing their opinion that's totally nonbinding except of course I can exert selective regulatory scrutiny if I feel like it" is not a get-out-of-jail-free card.
The government notifying Facebook that someone posted content contrary to Facebook's TOS doesn't violate the rights of the person violating said TOS. You never had a right to post content that violates the TOS you agreed to in the first place.
You do have a right to share that same content on your own website and the government would have no right to make you take it down.
In no cases were people unable to express their opinions. They were unable to create posts or comments contrary to the terms of service of the site they were using to share said opinions. Much like neither of US may herein violate the terms of Hacker News.
I think you can see how a court might look at that as laundering unconstitutional actions through a private entity and hold the government to a higher standard than that.
That the government was "just expressing their opinion that's totally nonbinding except of course I can exert selective regulatory scrutiny if I feel like it" is not a get-out-of-jail-free card.