If I recall correctly the First Amendment came after Article 1 Section 7 and limits the ability of the Congress to abridge the Freedom of Speech of all of it's Citizens. An amendment to the constitution limiting the authority of congress supersedes any prior authorization in the Original Document.
Therefore while the Congress can make rules for the Government and Regulation of land and naval forces, it cannot include in those rules any blanket prohibition of Free Speech and Assembly or Religion or freedom of the press (In this case the freedom to post opinions on line).
Congress must have a stated COMPELLING reason to limit the free speech of any Citizen. A blanket prohibition against political speech is neither necessary or compelled by any purpose for which such a blanket prohibition would be served.
Good order and discipline does not require that soldiers and Marines give up their right to express their opinions on political topics not directly related to their service in the armed forces.
The First Amendment specifically prohibits congress from abridging the freedom of speech as part of its authority to make rules for the Government and Regulation of the armed forces.
Do you think that Article 1 Section 7 is not subject to the Bill of Rights? Is that the attitude I'm hearing here?