The Bible was not the ONLY source of our laws.
While many of our laws are based on principals that can be found in many religious texts including the bible, those are universal. Many things required in the bible are prohibited by our laws. The bible was not the source of our laws, as Mahz points out.
The founders were well aware of the atrocities perpetuated through the ages based on nothing more than a few passages found in the bible. The wanted to keep the bible out of the law, not to enshrine it there.
"Among the most detestable villains in history, you could not find one worse
than Moses. Here is an order, attributed to 'God' to butcher the boys, to
massacre the mothers, and to debauch and rape the daughters. I would not
dare so dishonor my Creator's name by (attaching) it to this filthy book
(the Bible)." "It is the duty of every true Deist to vindicate the moral justice of God
against the evils of the Bible."
"What influence in fact have Christian ecclesiastical establishments had on
civil society? In many instances they have been upholding the thrones of
political tyranny. In no instance have they been seen as the guardians of
the liberties of the people. Rulers who wished to subvert the public liberty
have found in the clergy convenient auxiliaries. A just government,
instituted to secure and perpetuate liberty, does not need the clergy."