In essence, laws will always be based on religion, they can be based on the religion of "divine man" or "divine God".
As a Christian, I simply cannot be a secularist.
MAYBE ONE IS DIAMETRICALLY OPPOSED TO THE OTHER?! MAYBE BOTH SYSTEMS HAVE "MORALS" AND SHARE PARTS OF ONE ANOTHER?
That isn't so weird is it?
To answer the OP, of course they should be separate. We escaped "God ordained royalty" and religious tyranny to form this country. Our fore-fathers knew exactly what the problem was. They chose reason and evidence over faith and a complete lack by faith's very definition. Our judges can tell you what is reasonable in that they demand evidence....
Article VII
Done in Convention by the Unanimous Consent of the States present the Seventeenth Day of September in the Year of our Lord one thousand seven hundred and Eighty seven and of the Independence of the United States of America the Twelfth. In Witness whereof We have hereunto subscribed our Names
"Lord" refers to Jesus Christ.
The reality is that the Declaration of Independence is very important to understanding our founding principles. The Bill of Rights was actually created as an answer to the question "How may we legally protect the rights as outlined in the Declaration"
Article VII
Done in Convention by the Unanimous Consent of the States present the Seventeenth Day of September in the Year of our Lord one thousand seven hundred and Eighty seven and of the Independence of the United States of America the Twelfth. In Witness whereof We have hereunto subscribed our Names