The "free exercise" and "establishment" clauses
presuppose an understanding of and acceptance of the diversity of Christian religious practice in colonial America. Whether Anglican, Congregationalist, Catholic, or Baptist, the exercise of religious faith and faith-centered life is referenced. When the writings of the framers and founders are explored this becomes a bit more clear. If totalitarian secular humanism was intended, this was a pretty strange way to go about it.
The Carl Sagan/Norman Lear/Madalyn Murray-O'Hair-style of secular humanism does not get a boost from this.