Just medium-to-high density by UK standards around existing larger train stations would do an immense amount to alleviate the UK housing crisis.

I used to live on a road with ~660 houses. The road, the houses, and the yards combined took up ca. 40,000 m^2. Near the local well-connected train station, a few new-builds in the 20~ floor range added more homes than that entire road took up in ~2,000 m^2.

On top of that, because of its location, the strain added on transport was far less - most people would be a short walking distance from both shops and commuter trains to the centre.

There are hundreds of major transit hubs like that in the UK where you could easily add do relatively modest hubs of higher-density housing and add a massive amount of capacity.

What's lacking is the political will to solve the massive problem of house owners who have been trained to see rising house prices as financially beneficial to them.

When most of those house owners are in an older demographic more likely to vote, it's a huge challenge to fix.

I interpreted that comment as not meaning density but instead geographical concentration.

WFH was an opportunity to escape from geographical concentration which is the main cause of the high cost of housing.

Why is it supposed to be good? Having lived in a (relatively small) city and in the countryside, I vastly prefer the countryside and actually find it more convenient in a lot of ways. An example would be the shops are a lot bigger as the land is cheap, so a 20m drive in the country gets me to a massive shop, but in the city half an hour on a bus or a 15m drive gets me to a much smaller one.

If by 'drive' you do not mean bike (or maybe moped), then that way of life does not have a future (or even present, for most people).

Density itself is good for infrastructure, but empirically it seems that we cannot exceed some level. Singapore or Hong Kong for example desperately need more density but it seems impossible to do so.

Then there is the question of wasted resources. We spent all of these resources to build up Detroit. Now what?

Paris, where I live, is three times as dense as Tokyo... The entire city is mixed-used 6 storey buildings.

It's probably because Paris, officially, is the very small hypercenter of the Parisian metropolitan area. Whereas Tokyo is the actual total metropolis. Just look up the population of both. Paris is 2 millions whereas Tokyo is 14 millions. If you were to consider the whole Paris metropolitan area then the population is 11 millions.

Yes but the average size of a flat in Paris would be shocking to an American.

500 square feet for a couple is standard (that would be seen as a small appartment in the USA) and living in 300 square feet or less is fairly common for someone single.

To be fair, the average size of a flat in Paris is shocking to Frenchmen living outside the city.

Same thing with New York I guess. I had a cousin move from Paris to Manhattan, and it didn't really feel like an upgrade.

tokyo has 20x as much land as tokyo. If you just counted tokyos densest 40 sq miles it would be denser than paris