That's not exactly true, your freedom of speech rights are limited by UCMJ, especially under Articles 82, 88, and 134, but not eliminated. You still have a right to attend peaceful demonstrations and such. It is, however, shameful how we treat military men and women in this country. As far as I am concerned, they should have just as many rights as any one else.

Also, it's not really a counterexample, because you do not sign away your rights when you sign the enlistment papers, you loose some of your rights by simply being part of the military. People who where drafted back in the 60s also lost had their rights limited, even though they did not voluntarily sign any papers or agreed to anything.

Further, this is an act of the government, and not a civil contract. No CIVIL CONTRACT can take away ANY of your constitutional rights.