I specifically mentioned sunk cost because it can be fallacious. I was aiming to get ahead of that. Not every sunk cost is fallacious, and that's why I went into depth about sunk costs vs opportunity costs.

And again, on an INDIVIDUAL level I agree with you. Individuals don't have that kind of impact on demand as something like a ban of ICE engines, or broad adoption of them to the point of masses of people looking to buy at the same time does.

Individually, buy one as soon as it makes financial sense for you, ideally when you'd be buying a car anyway.

Systemically, buy one when your car dies, keep your running machine for as long as possible.

Specifically the opportunity costs I'm referring to are manufacturing related. Right now, producing EVs is more costly than producing ICE cars, in terms of carbon footprint. If too many people adopt too quickly, it results in more being produced while the manufacturing process is still shitty.

There's a problem with the "pass down the cars" thing too. At the end of that chain is still a car being decommissioned. If it's still usable, that's a higher net carbon footprint. A new EV still had to be produced for that chain of used car sales to go through.