It's not secure because any widely rolled out physical layer is by definition compromised. All infrastructure in a country is beholden to that country's govern

It's not secure because any widely rolled out physical layer is by definition compromised. All infrastructure in a country is beholden to that country's government, and that will never change. Any attempt to put encryption into a widely used physical layer will fail, because no committee will agree on an effective implementation that actually works (governments WILL subvert any committee). Governments will insist upon backdoors or sniffers, and hardware has the disadvantage of being in one physical place, easily targeted by a government. The physical layer is compromised, and always will be.