Why must there be an "it" through which TEM waves proagate? Why cannot
they propagate through nothingness?

Because the only thing that can propagate through
nothingness is nothing. That should be clear to
the most casual observer.
--
73, Cecil http://www.w5dxp.com

So you are trying to tell me that if I completely evacuate a sealed glass
jar it then contains space? That's like saying the absence of light is
darkness. True as a conceptual description of nothingness. If you choose
to rename nothingness, does that mean it aint nothin? You guys have too
much time on your hands.