You could not be any further from the truth when you state that the idea that people can do whatever they want when in positions of political authority is a liberal idea. That is the antithesis of liberalism. Liberalism is based on the idea that there is an absolute natural moral law established by God that essentially governs the universe as much as the laws of Physics do. As such democracy is irreconcilable with liberalism. Liberalism advocated republicanism or constitutional monarchies where Parliaments ruled, not majority rule. And of course liberalism is built on the belief that limited government confined by natural law is the only moral government. As such social contract theory is one of the foundation principles of liberalism. The idea that government can strive for a "higher ideal" is an idea popular among the enemies of liberalism such as Marx. Marx railed against Liberalism in the Communist Manfiesto because it destroyed the power of the state to make a classless society possible even on paper.
And about the people overthrowing their government part... perhaps you missed studying the English Civil War. You know, the one where Cromwell's forces overthrew the monarchy and established the Commonwealth?
I said the founders "adopted much of this philosophy.
Which French philosophers do you think influenced them more than Locke? I find your assertion interesting as it is something no one else has made that I have seen at least.