As you say, free speech. So youll have to find another way. Ideally we need voters to be informed, and thus not vote in whoever promises them the most stuff. But that will never happen, so where do you go from there? You cant remove free speech, you cant elect uncorruptable politicians. One solution would be to shrink govt such that they have little power to sell, but that still requires getting the right people elected.

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"To take from one, because it is thought his own industry and that of his father has acquired too much, in order to spare to others who (or whose fathers) have not exercised equal industry and skill, is to violate arbitrarily the first principle of association, "to guarantee to everyone a free exercise of his industry and the fruits acquired by it."

-Thomas Jefferson