Have you watch the movie "Jarhead"? It's from real life story about marine who serve in Iraq on the first dessert storm operation. And there's part of the movie where there's some media who come to Iraq to interview the marine, then the sergeant tell them not to tell any truth but only say something full of spirit and supporting the nation. The dialogue gone like this :
Kruger: This is censorship.
Sgt. Siek: This is what?
Kruger: Censorship. You're telling us what we can and can't say to the press. Thats un-American.
Anthony 'Swoff' Swofford: Yeah, what about freedom of speech? The Constitution?
Sgt. Siek: No you signed a contract. You don't have any rights. You got any complaints you complain to Saddam Insane and see if he gives a *cabbage*.
Kruger: Why that's exactly what Saddam Hussein does. You're treating us the same way.
Sgt. Siek: You are a marine. There is no such thing as speech that is free. You must pay for everything you say.
LOL
Any organization, any job - this same basic tenet holds true. I cannot badmouth the organization I work for without having to worry about the consequences. When you sign a contract, as you do when you join the military, you agree to certain rules and restrictions. In the US, if you don't agree to the rules, you certainly do not have to sign up. It's that simple. But if you agree to them, then you have no right to complain when they infringe upon your desire to do what you want. The First Amendment only says that Congress shall pass no law abridging one's freedom of speech. It does not mean that a contract - a legal, binding document entered into voluntarily by two parties - cannot place restrictions on those freedoms. Also, keep in the mind that the intent of the Constitution is to limit the power of government, not to guarantee rights and freedoms.
The other thing, 'Jarhead' was a movie, not a documentary. The fact that it was presented that way indicates that there has been some embellishment and, with as with any embellishment, an introduction of a bias - the setting up of two parties as the antagonist and protagonist. It makes for a much better story. To see what I mean, watch a documentary on D-Day and then watch the movie 'The Longest Day.' They both are based on the same event, but you get a much different picture as you watch each.