Must have been public school. This country was founded upon the morals of the Christian tradition. The Ten Commandments were a basis for some of the most basic laws in our society; such as killing, adultery, theft, etc. Doesn't the Congress need a majority to pass legislation? The Congress is supposed to be representative of the population as a whole. Our founding documents are based upon the teachings of Christianity, like it or not. "Majority rule" is simply a phrase to describe representative government (as set up in the Constitution). Must be the public school thing again.
Last time I checked, if the US was "majority rule," then Gore would have won the 2000 presidential election. Bush won the election because the US is a representative republic, and not a "majority rules" democracy.
In general, yes. The whole point of the Constitution, however, is that some questions are beyond the reach of the majoritarian process, because an elected legislature can run roughshod over the rights of the individual. The Establishment Clause is one such provision. It is irrelevant whether the majority of Americans are Christian. The Establishment Clause prevents the Government from being "Christian."