What have political philosophers said concerning the idea that money equals speech? It seems to me that money is a means of exchange and carries no inherent ideas or appeals, perhaps other than the metamessage that larger the sum the greater the purchaser's potential means and influence. A purchase is not persuasion. It seems to me that money allows (in the case of a televised political ad, for example) for a message to be developed, produced, distributed, etc. Money, then, facilitates speech, but is not itself speech. What arguments have I missed?

I doesn't seem to me that you've missed anything. The claim 'money equals speech' is best understood, I think, as a shorthand way of making the point you make here about money, that it "allows (in the case of a televised political ad, for example) for a message to be developed, produced, distributed, etc. Money, then, facilitates speech."

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