"A democracy cannot exist as a permanent form of government. It can only exist until the majority discovers it can vote itself largess out of the public treasury. After that, the majority always votes for the candidate promising the most benefits with the result the democracy collapses because of the loose fiscal policy ensuing, always to be followed by a dictatorship, then a monarchy."
-attributed to both Alexis de Tocqueville and Alexander Fraser Tytler, but maybe said by Elmer T. Peterson
chart from this blog post