Uncontrolled re-entry of a single large object would, I think, be preferable to re-entry of dozens of them.

I guess the opposite. It won’t be a single object for long, after the final re-entry has started, so I say give the breakup process a headstart! (Well, I don’t actually. I actually assume it’s a bad idea, and would like to know why. Geopolitics not included.)

No agreement would have any effect on the headlines saying “US allows its spacestation to crash on city, killing 800 people”.

Agreed. However, I’d bet my life that this wouldn’t happen. Both literally (though I’d need good odds, and a high valuation for the value of my life!), and in the sense that I (and all my loved ones) live under the ISS’s flight path.

I estimate (partly based on this) that less than 0.6% of the earth’s surface is “built-up”. (Though the ISS doesn’t fly over it all equally, so call it 1%.)

For what it’s worth (nothing?!), I used that figure, and some other guessed figures, to guess that the expected value of the number of people killed per uncontrolled ISS reentry is 0.05, so on average needing 20 space stations to kill 1 person.