[avar]

Your friend may understand environmental science, but clearly not economics.

If you don't keep your car you'll sell it. You won't be moving the needle on how long it'll take to amortize that initial manufacturing cost, it'll just happen with someone else driving it.

Likewise if you don't buy a new car someone else will, you're not going to move the needle on the overall supply.

I don't recommend buying new cars, but if you consider the above it's pretty much pollution-neutral.

All you're really doing is paying a premium in order to be the first in a long line of owners to drive that vehicle.

[PopAlongKid]

You appear to be making an unfounded assumption that regardless of how many owners it has, any given vehicle will remain on the road the exact same number of years.

If an owner decides to keep and maintain their car longer than they would have in the past, that car will stay out of the junkyard longer and therefore reduce the need to produce new cars. They will use some of the money they would have spent on a new car to keep the old one going longer, and still pocket the rest of it as savings.

[avar]

I'm not, I'm assuming it'll average out.

It's no more likely on average that the current owner is an enthusiast that's extending the usable lifetime of the vehicle than the next owner.

[rurp]

Most households keep a fairly fixed number of vehicles. Selling more moderately used vehicles into the used car market will result in more old vehicles being retired sooner.