If people in general are so swayed in their voting by mere advertising, "democracy" itself is the problem.
Be it one human or 200 million humans involved in political decision-making, human nature is the flaw in any government instituted among men. "Democracy"--generically speaking, meaning the practice of popular voting by the general population as the means of setting the course for a community or society--seeks to maximize the impact of human nature in governance. If human nature is so susceptible to propaganda that all the money spent on political campaigns makes a difference, then this form of government is not simply flawed (as are all things among humans), but in fact ultimately counterproductive in pursuing the legitimate purposes of government as outlined in the various governing documents produced down through history. Thus, say what we will when we weigh strengths and weaknesses of different forms of government, a conclusion not reasonably deniable by anyone (and libertarian arguments to the contrary deny human nature, and thus are NOT reasonable) is that "maintain...