Nonesense and slop.
All this means is you are too intellectually lazy to care, or you sense the conclusion before you start and you are not honest enough to accept it.
"Plain meaning", in any field, makes the text putty in the hands of the interpreter, and you know it. It produces crap in New Testament studies, crap in literary criticism, and crap -- which you probably complain about elsewhere -- in constitutional law.
When I read Shakespeare, and he uses a word, I don't ascribe the meaning to that word which is "plain" to me -- I look the word up, I find out what it meant to him, and thus I am really reading Shakespeare. Looking it up and otherwise finding out what it meant in his century and culture is not "channeling" (your strawman argument) -- it is SCHOLARSHIP. If you don't do it, or rely on someone who has by reading their marginalia with the play, you can still enjoy the play, of course. But no further; you can't take part in an argument about the meaning of a detail in the play by saying "well, the plain meaning of the phrase to ME IS..." -- you'd be laughed out of the classroom. In a rigorous classroom you'd be told "shut up. We don't care what the words mean to you. Talk about what they meant to the Bard." You can take Shakespeare and supply your own meaning, but the IT'S NO LONGER SHAKESPEARE. IT'S YOU.
Now along comes the Constitution. Somehow, now it's o.k. to just make up meanings. The guys who wrote it meant one thing, and we know that very well because of what they said in commentary or what they dd or didn't object to in their day. (say it with me: SCHOLARSHIP)
But somehow we're allowed to disregard their meaning, but take their words and ascribe to them NEW MEANINGS, which, of course, are just "plain meanings" to us -- but then it is no more the Constitution we're discussing than if we were discussing Hamlet by saying "well, when I SAY 'to be or not to be', here is what I MEAN".
You're lazy. You're lazy, and you happen to like the result this time, but others can interpret other Constitutional words by their "plain meaning" ('MILITIA?" FREE SPEECH") another time and on another issue and you won't like it and you have no grounds to protest.
But you will, of course, and that will just make you a lazy hypocrite. "Plain meaning" is the petard on which you yourself will be hoisted.