Ah, I took your position as being able to determine screen size (or have it determined automatically through CSS or some other hands-off mechanism) itself was also unneeded, not just that JS should not have this capability.
I can get behind most of what you say - as long as we are talking about simple, presentation based websites.
Where I think there's a breakdown in this view is when you consider complex web applications, including games. At that point, I believe some level of inspection capabilities are required, if we desire to have complex web apps delivered through the internet. I'm by no means sold that on-demand web delivered code is necessarily a good thing though. There's far too large a surface area to adequately secure while still making it useful, IMHO.