Despite what religious fundamentalists and the misinformed will tell you, the United States was not founded on Christianity. The founding fathers were largely DEISTS--the closest equivalent today would be Unitarian Universalists. The US Constitution does not mention God once, and there is only a fleeting reference to divine providence in the Declaration of Independence.
The bedrock principle of the federal government has been one of NEUTRALITY with respect to religion, which is precisely what the First Amendment was written to ensure. That neutrality has been chipped away since 1954 when "In God We Trust" was put on the money and "Under God" was added to the Pledge of Allegiance. Bush's faith based initiatives have further eroded the First Amendment.
In am of the Chrisitian faith. However, I have no desire to see that faith forced upon anyone. I am also cognizant that the separation of church and state has part of its basis in the New Testament ("Render to Caesar what is Caesar's and unto God what is God's"). That seems to escape some of the more fundamentalist Christians.
I have no desire to see the United States morph into a Christian Iran, and I suspect the vast majority of Americans agree with me, whatever their personal religious beliefs.
“The government of the United States is not in any sense founded on the Christian religion.” - Treaty of Tripoli, signed by John Adams (giving it full power of law - read the Constitution)
“Twenty times in the course of my late reading, have I been upon the point of breaking out, ‘this would be the best of all possible worlds, if there were no religion in it.’” - John Adams
“Believing with you that religion is a matter which lies solely between man and his God, that he owes account to none other for his faith or his worship, that the legislative powers of government reach actions only, and not opinions, I contemplate with sovereign reverence that act of the whole American people which declared that their legislature should ‘make no law respecting an establishment of religion, or prohibiting the free exercise thereof,’ thus building a wall of separation between church and State.” - Thomas Jefferson
“...an amendment was proposed by inserting the words, ‘Jesus Christ...the holy author of our religion,’ which was rejected ‘By a great majority in proof that they meant to comprehend, within the mantle of its protection, the Jew and the Gentile, the Christian and the Mohammedan, the Hindoo and the Infidel of every denomination.’” - Thomas Jefferson
“Our civil rights have no dependence on our religious opinions, more than on our opinions in physics and geometry. . . .” - Thomas Jefferson
“The legitimate powers of government extend to such acts only as are injurious to others. But it does me no injury for my neighbor to say there are twenty gods, or no god. It neither picks my pocket nor breaks my leg. . . .” - Thomas Jefferson
“The day will come when the mystical generation of Jesus, by the Supreme Being as his father, in the womb of a virgin, will be classed with the fable of the generation of Minerva in the brain of Jupiter.” - Thomas Jefferson
“Religion and government will both exist in greater purity, the less they are mixed together.” - James Madison
“My parents had given me betimes religious impressions, and I received from my infancy a pious education in the principles of Calvinism. But scarcely was I arrived at fifteen years of age, when, after having doubted in turn of different tenets, according as I found them combated in the different books that I read, I began to doubt of Revelation itself.” - Benjamin Franklin
“It is the duty of every true Deist to vindicate the moral justice of God against the evils of the Bible.” - Thomas Paine