Correct. I'm being completely serious, with the exception of the remark about exploding limbs (obviously).
JS has more features than it deserves for learning about and (critically) sharing information about the host platform. Yes, you can still learn some things as a website operator by watching what browsers load/don't load, and what they put in their requests.
Edit: I should hasten to add that there are other concerns beyond privacy, like accessibility and the fact that a web page has no bloody business deciding that I'm likely running an iPad and therefor I shouldn't have access to X or Y. This is dumb, and contrary to the idea of the open internet. It's the same thing that's wrong with this EME nonsense.
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.