Sure, it would be impure, and not top-to-bottom reproducible, and you don't personally have to do it. But it's a choice to avoid a compromise, not an impossibility precluded by the laws of math or anything.
Regardless, I no longer really sympathize with Free software's concept of a "freedom" that results in either (1) obscure purity, or (2) benefits large corporations at the expense of the rest of us.
RMS was economically naive, despite his counter-cultural leanings; I can't help but wonder what Free software would have looked like if he'd imagined the likes of MS/Amazon getting rich off it while creators get a pittance. We can't all have free-floating MIT jobs.
I'm writing my comments in the first person, because I have actually made the effort to investigate this in the past, more than once.
This is precious little to do with some kind of abstract purity. Hell, I've packaged Tensorflow and CUDA crap, which is as far removed from purity as it gets.
It gets a little tiring to read about values that are projected onto Guix, that I can't find in my own work.