Would they assign a set of "morals" and stick with them?  The founders did through a recognition of God's will. Could these good and moral people apply their morals universally? God has, and the founders recognizing those morals stated so when declaring

"We hold these truths to be self-evident, that all men are created equal, that they are endowed by their Creator with certain unalienable Rights, that among these are Life, Liberty, and the pursuit of Happiness."

The undeniable statement by our founders that there are things mans laws, relative developments, and changing society cannot take away is that true "rights" are indeed assigned by our Creator; our God.

There can be but one set of universally recognized truths, and that is when we are conceived, our nature is to live, otherwise we would die without developing. It is to be free, otherwise we would stand still, would not move, would not think.  It is to pursue, create, acquire, or we would not make shelter, feed ourselves, develop skills. There is no society on earth where these things so eloquently stated in Jefferson's drafting of the declaration are not relevant, or not true.

No place at all.

Even freedom loving atheists ought to consider this a good thing.  Atheists who consider the supernatural impossible, improbable, unscientific can recognize that those truths are indeed self evident, even if allowing for the "Creator" to be described only as "Mother." But mom cannot rule mankind. Mom can be altered and changed, and can presume to take away those rights as we have seen in the embellished news cycles of late. So even Mom would not be sufficient for those who would desire a consistent platform of rights as recognized by all who live, move and pursue.

And we return to the statement as presented by this CFI group that "you don't need God."

What then do we need?  What then binds humanity through different governments, both benevolent and abusive?

If one cannot rely on the truth that God our creator, has given us certain rights, then they would not exist.  If the argument becomes one where government grants those rights, then cannot a government take them away? If the standard is the relative nature of whatever government exists, then the rights we see as self evident truths become simply "permissions."

Logically, we DO need God. Atheists need God. Mankind needs God.