Voting for bread and circuses
Voting for bread and circuses refers to a popular belief that the common citizens in a democracy will ultimately be its undoing when they discover that they can vote for common savings to be dispersed. Another very similar expression is the Tytler quote, which argues (also without evidence) that democracy "can only exist until the voters discover that they can vote themselves largesse from the public treasury."
It comes from a quote by Robert A. Heinlein (emphasis added):
The America of my time line is a laboratory example of what can happen to democracies, what has eventually happened to all perfect democracies throughout all histories. A perfect democracy, a "warm body" democracy in which every adult may vote and all votes count equally, has no internal feedback for self-correction. It depends solely on the wisdom and self-restraint of citizens... which is opposed by the folly and lack of self-restraint of other citizens. What is supposed to happen in a democracy is that each sovereign citizen will always vote in the public interest for the safety and welfare of all. But what does happen is that he votes his own self-interest as he sees it... which for the majority translates as 'Bread and Circuses.'
'Bread and Circuses' is the cancer of democracy, the fatal disease for which there is no cure. Democracy often works beautifully at first. But once a state extends the franchise to every warm body, be he producer or parasite, that day marks the beginning of the end of the state. For when the plebs discover that they can vote themselves bread and circuses without limit and that the productive members of the body politic cannot stop them, they will do so, until the state bleeds to death, or in its weakened condition the state succumbs to an invader – the barbarians enter Rome.
Mine was a lovely world – until the parasites took over.
It is also found here.
This source ascribes it to the character Lazarus Long, but it is actually Jubal Harshaw, whose "time line" has the same history as our own.
There is a similar quote attributed to Benjamin Franklin but probably not written by him:
When the people find they can vote themselves money, that will herald the end of the republic.
This idea is commonly used as an argument for:
- restricting the vote, since the "common man" cannot be trusted to make responsible decisions about the allocation of a nation's wealth.
- reducing public services and entitlements, since that is the "common people" reallocating other people's money for themselves.
The common citizens in a democracy will ultimately be its undoing when they discover that they can vote to acquire the country's wealth for their personal benefit. The United States in the early 21st century is an example of this: Lower income-earners pay a much smaller percentage of the government's tax receipts than do higher income-earners. 
- This is called progressive taxation, which actually helps sustain society.
- It is actually the upper earners who have by far the most influence over political decisions.
- Social programs and entitlements have a history of being reduced steadily, per capita, over the past few decades.
This argument is proven true by the collapse of the European socialist state. Decades of unsustainable spending has begun to collapse on itself and the "commoners" are rioting at the suggestion of later retirements and fewer benefits.
- The European economic collapse has been all the more rapid due to austerity measures -- the opposite of "bread and circuses".
This is basically a ludicrous and poisonous argument which seems designed to appeal to the selfishness and elitism that are in plentiful supply at all levels of income.
There is no evidence to support the idea that the "commoners", or their equivalent in whatever democracy is under discussion, have been its downfall through this mechanism. Just looking at the evidence of the US, it would appear to be specific members of the upper class who have "voted themselves bread and circuses" and been the primary cause of the recent economic crisis through their support for multiple simultaneous wars (US-Iraq War, US invasion of Afghanistan), deregulation of the banking industry. and other political efforts.