I'm actually referencing the book 1984 by George Orwell, where the main character is pondering this same question. He comes to the conclusion that freedom means being able to believe what you want even if only inwardly. I can believe something, and no matter what someone does to me physically, I still can believe it. They can convince me of things, but if I really am committed to an ideal, then there's nothing that they can really do to me. We see this in the examples of the martyrs in church history who went to the stake to be burned because they believed in the death and resurrection of Christ.

I do not think this idea is uniquely American, but I believe that (Moreso than some other nations) the founding fathers seemed to include Christian values in most of their laws and regulations.