Says right there in black and white....

Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof; or abridging the freedom of speech, or of the press; or the right of the people peaceably to assemble, and to petition the Government for a redress of grievances.

Update: Thomas Jefferson in a letter to the Danbury Baptist association in Connecticut.:

Believing with you that religion is a matter which lies solely between Man & his God, that he owes account to none other for his faith or his worship, that the legitimate powers of government reach actions only, & 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 & State.

Update10/21: The Dunning–Kruger effect which is apparently the strongest in Americans:

Kruger and Dunning proposed that, for a given skill, incompetent people will:

tend to overestimate their own level of skill;

fail to recognize genuine skill in others;

fail to recognize the extremity of their inadequacy;

recognize and acknowledge their own previous lack of skill, if they can be trained to substantially improve.