You are absolutuely right that no one has a right to be on the radio, but one does have a right (yes, first amendment in my opinion) to expect a valid contract you have, and earn a living thru, not be tossed aside - and you lose money - by a politician (or group of politicians) just because they didn't like something you said.
Now, honestly, I haven't gone back and checked Levin's actual comments. If he just said something like, "I don't think this is the kind of talk that our serviceman should be hearing", as an opinion (albeit, a powerful one) expressed to those who determine the programming on Armed Forces Radio, which the programmers can then listen to, or ignore, as they decide what if anything they want to do (legally/contractually) with Rush's show on their station, then I don't see a problem. But it is a problem, if Levin used his power as an upper eshelon member of the government to get Limbaugh's show pulled. Yes, fortunately he PROBABLY doesn't have the power to that, but it is still telling if he seems to think he can.
No opinion on my Media Matters canundrum?
And there is your problem. The First Amendment does not cover Contracts.
And when you assert it does you immediately invalidate your whole argument. Use the proper argument and you give the left no cover, use the wrong one and they can dismiss your whole premise.
Why do you wish to give the left ammo to dismiss your assertions?