That's quite a question.
I’m not enough of a student of history to be able to make an informed hypothesis as to the origins of the issue. I can say, however, that the vast majority of people do not realize that the United States was not actually founded on Christian principles.
The First Amendment
Congress shall make no law respecting an establishment of religion...
Article VI, Section 3
...no religious test shall ever be required as a qualification to any office or public trust under the United States.
The Constitution plainly states that the Founding Fathers wanted no basis or reliance on religion. The expectation was to protect religious freedom by wholly separating the government from religion. In this way a religious majority could never legislate their faith on others.
Religious politicians often counter the separation of church and state by claiming that, in this country, we have freedom OF religion, not freedom FROM religion. This is false — those who have no religion are just as protected by the Constitution as people of faith.
I think the common-knowledge belief that America is based on Christianity comes from certain aspects of our past. We have always had a Christian majority in this country. Many of our first settlers were, in fact, puritanical Christians fleeing religious persecution in their European homes (the irony of Christianity persecuting non-Christians while claiming to be persecuted themselves is lost on most). Certainly the Cold War years ingrained a false religious heritage. Under God was inserted into the Pledge of Allegiance, and the Commies were demonized as Godless.
The truth is, of course, that the Founding Fathers were fiercely opposed to any kind of religious influence in the government.
John Adams (the second President of the United States)
Adams signed the Treaty of Tripoli (June 7, 1797). Article 11 states:
The government of the United States is not in any sense founded on the Christian religion.
From a letter to Charles Cushing (October 19, 1756):
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.’
From a letter to Thomas Jefferson:
I almost shudder at the thought of alluding to the most fatal example of the abuses of grief which the history of mankind has preserved the Cross. Consider what calamities that engine of grief has produced!
Thomas Jefferson (the third President of the United States)
Jefferson’s interpretation of the first amendment in a letter to the Danbury Baptist Association (January 1, 1802):
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.
From Jefferson’s biography:
...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.’
Jefferson’s The Statute of Virginia for Religious Freedom:
Our civil rights have no dependence on our religious opinions, more than on our opinions in physics and geometry....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.
If one studies the actual beliefs of the Founding Fathers, it quickly becomes apparent that America was never intended to include the religious stigmas and rules it has today. Various examples of legislated Biblical morality (sodomy laws, including laws against oral sex, laws against the selling of sex toys), for instance, are still on the books in some states, because the people and legislators either misinterpreted the Founding Fathers design, or simply ignored it.
When it comes right down to it, I think the root cause may be the I’m right, and you’re going to Hell if you disagree mentality of many Christians. Some see the establishment of America as a Christian nation to be their God-given duty, and don’t recognize the right of others to have their own beliefs.
I, too, wish the attitudes of the Founding Fathers were prevalent today. I certainly don’t want a government that makes its decisions based on faith —
only 33% of people are Christian, after all.
™ Version 4.2