"A democracy cannot exist as a permanent form of government. It can only exist until the voters discover that they can vote themselves largess of the public treasury. From that time on the majority always votes for the candidates promising the most benefits from the public treasury, with the results that a democracy always collapses over loose fiscal policy, always followed by a dictatorship."
supposedly from The Decline and Fall of the Athenian Republic, c.1799 but no book has been found.
Questionable. See http://www.snopes.com/politics/quotes/tyler.asp