Our shared cultural values, assuming we had them, to wit, that we had made the same a priori assumptions, whether draped per se with theology or not.
You have prescribed a lifetime of slavery for yourself and your offspring. Your reasons would never instill a righteous fear into the hearts of anyone wishing to control and dominate you. The only way you could free yourself would be through the use of brute force. This would be a world of survival of the fittest, where the strong control the weak. It would be a world where man himself decides what is and what isn't right, or what is and what isn't freedom.
Those brave souls who founded this nation didn't believe we live in such a world. My freedom and yours stem from what they believed in. Had they believed as you currently do, there would not have been an America to live in.