> How do you figure that? Single family homes are inherently enormously costly - more concrete, more energy to heat or cool, and more roads to access them.

Single family homes can be wooden frame on light foundations, tall buildings can't. Single family homes can be demolished and rebuild every passage (meaning 50-80 years) so they can be as efficient as "relatively recent" tech allow, tall buildings are a nightmare to evolve. I'm Italian, having left years ago a typical large enough apartments in the north-west of the country for a home in Sweden of similar size. The some in Linköping use LESS energy than the old apartment. Now I'm living in the french Alps, a new wooden frame home, about twice the size of the old one and I consume FAR LESS. Evolvability matter, much.

Here I have an EV and domestic p.v. in an apartment I've had a garage, but no p.v. possible, also consuming space for a heat-pump water heater and for main heating is not that easy, in a home no issues.

Not only, in term of mere raw materials just grab a project of any high rise buildings and compare that with any single-family home project multiplied by the number of apartments: you'll easily see that the high rise building demand MUCH MORE materials than many homes.

> A dense city is the place where ebikes or golf carts are most practical

And they demand large supply chain as well, witch means highways, railways of a significant size, because people need to eat as well and they are many in a restricted area, enlarging even more the infra costs... Roads in a spread areas are lighter, do not demand much complex infra. Moving with light personal vehicles instead of moving heavy trucks, even if in smaller numbers, is FAR less consuming. The hard part is organize the logistics but with IT we can.

> Electrical transmission is extremely efficient, worrying about "local" electricity makes little sense. Metros in a city don't displace walking/cycling, they're displacing car use.

Electricity grids all over the world are LESS and LESS reliable due to growing demands, generation issues and climate change, there is NO WAY to keep them up reliably in a changing world, so the same for roads, rails, water supply and so on, that's why we talk about "resiliency", because modern countries, cities are damn fragile and inflexible.

> Low density cities/suburbs are the worst of both worlds for social life, IME.

beware US-style suburbs are horrific because they are residential only, you can't do anything else than stay at home or have a trip with a car. Mixed low density areas are another beast. Where I am now we are few homes spread in a dead-end road, but with a small park aside, few activities a 10' walking, a small lake a 12', a small river with enough water in the spring to canoe a bit on the north side and so on. It's far different than a big lot of homes and nothing else. So it's different the social life part: in large cities I normally not even know many if not most of my neighbors, here's families pass kids one to another normally, (almost) anyone cheers (almost) anyone else and casual parties in the garden are far common from spring to autumn. Something never seen in cities. At maximum there we go to a restaurant or a shopping center and so on.

> On average people in your position travel more, and in more environmentally damaging ways

In mere km-terms yes. In impacting terms no. I mean WFH I can recharge my EV almost on PV most of the time except winter. When I was in city I goes every weekends around, almost reaching the same kilometer range of now, but in more stressful way between traffic inside, highways and so on. Here I go calmly for beautiful roads. Roads that can be (some are, many are not) also full of small passages underneath to drain water and allow small animals to pass, having few small bridges to allow bigger animals to pass, cut the "forest" enough to obstacle eventual large fires to spread. No giant infra needed.

Keeping stuff to me means waste FAR LESS, well, because I'm attentive on what and how to keep. For instance means less packaging: I do not buy pre-cut cured meat under plastic, I buy entire hams, mortadella etc I cut in 2cm thick slices, freeze them, unfreeze one at a time, slicing them as thin as I wish. I do not buy bottles of wine but a couple of demijohns at a nearby producer, filling them with a pump, and i bottle them at home, with the same bottles every years. Similarly i buy olive oils in 10l batches filling the same bottles as needed. Of course I also eat salmon who happen to came from far away, so for shrimps, but some foods and beverage are local, and with far less packaging. Having more appliance if one breaks I'm not in a rush for another so potentially on scale the delivery of a new one and disposal of the old one can be scheduled for maximum efficiency. In case of a disaster the resulting emergency is far less "urgent" than in a city because most homes have a certain degree of autonomy and we are able to help ourselves and each others. So again, far less impacting.

It's not easy to dimension anything but try and i've no doubt you'll reach the same conclusions I've reached.