This is Stallman-esk far removed from reality.
I get the argument (also I think it nonsense) but what will rewriting a sites Javascript do about the server side? That would still be non-free. Or is the argument here that the backend and the API is not important because it's only generating HTML/Json/whatever and that's only "data" so you don't care about it. If so, I would turn that argument around and argue that the non-free Javascript is only an extension of the server side and is only generating data - the DOM.