There's a simple test. We can ask ourselves whether service people have the same rights as civilians. Can service people organize into trade unions? Can service people exercise the untrammelled freedom of expression that I can as a civilian? The answer to both of those questions is no. Obviously, as a matter of fact, service people have a different set of rights.
As to the suggestion that by joining the service you're voluntarily saying you're giving up your right to a fair trial, I don't think that's a fair way to characterize what I'm saying. I think the question is what we mean by a fair trial. If an employer seeks to dismiss an employee who belongs to a trade union, they have a different sort of trial from someone who doesn't belong to a trade union and is dismissed. Can we say that one is fairer? They're different because of the context.