Many of our founding fathers were Masons.
Jefferson was pretty agnostic, going so far as to craft is own bible which eliminated all the supernatural elements (ie: miracles, etc). Paine was an athest.
Pennsylvania was founded by Quakers as a religiously tolerant colony, Relatively speaking, to the religious authorities of Europe, they were heretics who deviated from the true orthodoxy.
After our Revolution, our own government - that of a Republic, was also looked upon by the European powers as an aberration, a government that deviated from the true and proper monarchies.
Relatively speaking, we were the deviants.
So I'd say that relativism and secularism had a place in the founding of America. (to an extent)
---
We were the deviants that changed the world. We made our deviations *THE* standard for the western world. If not the entire world.