The founders considered the morality that religion fostered,as an influence on the people governing.The 1st amendment said congress shall make no law telling you which religion to practice.Moral people want moral government,it's as simple as that.The majority religion at that time,and now,is Christianity.Half the signers of the constitution were ministers.
Of course I want a moral government, I also want one that governs based on fact, not fiction like religion. What you do in your own home is none of my business, when you start affecting my life because of your beliefs I have an issue.
"I have examined all the known superstitions of the world and I do not find
in our particular superstition of Christianity one redeeming feature. They
are all alike founded on fables and mythology. Millions of innocent men,
women, and children, since the introduction of Christianity, have been
burnt, tortured, fined, and imprisoned. What has been the effect of this
coercion? To make one half the world fools and the other half hypocrites; to
support roguery and error all over the earth."
-Thomas Jefferson
"The Government of the United States is not in any sense founded on the
Christian religion."
-John Adams in the Treaty of Tripoli
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, letter to Danbury Baptist Association, CT., Jan. 1, 1802