Other than the first class mail monopoly, the USPS also enjoys government 'protection' from having to pay gasoline taxes, parking tickets, vehicle registrations. and any other tax or fine that is imposed on a private sector business.
When the USPS decided to push into the package business around 1995 IIRC, UPS and FedEx started letter writing campaigns to alert Congress to the unfair advantage they would have with the ability to subsidize their losses with their first class mail monopoly. I haven't worked for UPS for a while now, but I do remember that was something management talked to us about, a lot!
But I don't really say anything that I'd care about coming back to haunt me. Granted right now we live in a semi-free speech society, and that could change but I still can't see a real problem with it.
Now to address the other part of your post concerning the government's surveillance, how about if it is going to be initiated for Law enforcement then restrictions should be in place, like warrants etc... So if a cop or federal agent comes to your house to talk to you about your recent postings online they have to tell you that it is being recorded or something similar to that.
Obviously there are going to be problems with abuse and such but it just doesn't seem to be stopping the government anyway.
The system was down for backups from 5am to 10am last Saturday.