The obvious downside is that all the UI elements are unnecessarily big for all the people not using touch.

Not anymore, a lot of apps (from browsers to the system UI) adapt to whether you have a touch screen and whether you use it. For example, Windows Explorer and Edge (and Chrome) still use (relatively-)compact widgets on touchscreen-less computers.

unless i misunderstand the implication as to their behavior on touchscreenful computers, this would seem to poorly address the concern upthread of explicitly expecting the touchscreen hardware, and thus the concomitant software annoyances, to become effectively unavoidable

Are you making this point from the context where you’ve never tried a touch screen computer?

This isn’t an unimplemented theory. You can head over to Best Buy right now and see what it’s like to use a touch screen laptop.

I feel like all this debate is taking place in an odd vacuum where a lot of us are talking about a bunch of potential problems with having a touch screen on a computer and all these problems are already resolved.

Maybe it’s similar to the whole iPhone duo thing where Apple users are just discovering all the caveats of a foldable phone, but we’ve already gone over all of it with competitors.