I'm afraid I simply don't follow this logic. I understand what you're saying, but I don't agree with it. Finite frequencies, whether regulated by the market or government, remain finite. So if it would endanger freedom of speech in the hands of the market, why doesn't it endanger freedom of speech with the government owning it?
Of course a finite number remains finite. That's not changed by who allocates the distribution of frequencies.
The point is that BECAUSE they are finite, if we were to permit some corporations to simply seize permanent control over the finite number of frequencies,
we would end up with NO available frequencies. But, because we ask the government to do the allocating of that finite number -- as leases -- the frequencies do
not become private property and forever unavailable. And because we employ the legal fiction that the airwaves belong to ALL of us, we can also impose conditions on HOW the corporations may use those LEASED airwaves -- such as forbidding them from denying us all access to the airwaves.
If the airwaves are OURS,
not the "private property" of ABC or MSLSD, then WE reserve some of our access to those airwaves. But as soon as the "market" does the allocating without the rules and regulations of the government, then the private property owners would inevitably and almost certainly lay claim to the right to completely EXCLUDE us in order to more fully exploit their "property."
If I own the land I have my house on, I can damn well exclude you. But if the government "owns" that land (in the limited sense of holding it FOR us), then when they LEASE that land to a company, they can absolutely place conditions on that lease (like, "thou shalt not restrict the public from the use and enjoyment of this land for X number of hours per week.")