I agree and don’t believe in the fiction either, but just because many or even most Americans do (or do not) believe in the fiction does not preclude it from be

I agree and don’t believe in the fiction either, but just because many or even most Americans do (or do not) believe in the fiction does not preclude it from being fair to describe it as “uniquely American” - in my mind OP was pointing out the origin of this worldview and the source of most of its advocacy and propagation, and I think they’re right?