McCain/Feingold as Argument Against Democracy

Let me follow up on the above with a couple thoughts. Isn't the dim, manipulable nature of the voter a premise of McCain/Feingold-like legislation? It strikes me that it must be. One can only “buy” an election by running a ton of ads if the ads really work. But is this a problem that can really be allayed by banning certain means of manipulation? If people are dim and manipulable, then their opinions already likely reflect their dimness and history as victims of manipulation. How is it, then, that an opinion changed by an advertisement financed by “soft” money is somehow less authentic than an opinion changed because of social pressure or a sophistical argument from the mouth of one's sister at a family reunion? How do restrictions on well-financed mass speech do anything to change the picture about the legitimacy or democratic character of outcome?