I'm normally on board with variations of this argument for things that don't significantly affect other people, but cars very much affect other people. Larger cars are more likely to kill other drivers, and especially bikers and pedestrians. The damage they do to the road is also a LOT more [1] so people who drive smaller vehicles and/or walk/bike are effectively subsidizing people who drive larger vehicles. They also cause more emissions meaning more medical issues and accelerated climate change.

[1]: https://en.wikipedia.org/wiki/Fourth_power_law

because cars have gigantic externalities

heavier cars are deadlier in accidents, they cause more damage to road surfaces, they require wider roads and parking spaces which consumes land, they require more resources to produce, they require more energy to operate, they produce more pollution, and so-on

The concepts of freedom and being comfortable in your car do not compute for non-Americans (and city-slicker-Americans)

That might be ok if people were responsible and not poorly trained to the task.

Also norms exist for a reason and resources on this very planet have to be shared with billions of other human beings.

Because cars have an impact on all of us, not just those driving them. These impacts range from tens of thousands of auto deaths every year to trillions of dollars in environmental damage that we will need to clean up eventually. Your libertarian fantasies are a poor match for the actual world.

Literally more road deaths