You left out one critical point. The smog that was choking major cities in the US and killing people would spread to many other parts of the US unless action is taken to stop the pollution that causes the smog.

In 1970, Republican President Nixon signed the Clean Air Act, and created by executive order the EPA, and within a decade significant progess was made in reducing the amount of smog creating pollution emitted in the US. And air quality has continued to be monitored for ozone producing chemicals, for ozone levels, and action continues to be taken to eliminate the sources of emissions that produce the smog producing ozone.

Still, if you go to places where almost no motor vehicles are allowed, places where few stationary sources of emissions are allowed, like the Grand Canyon, smog is not uncommon as a result of pollution from man-made sources hundreds of miles away. And that is something that is more common today than it was in the 1960s.

(In the 60s, the environmental fight was to prevent turning the Grand Canyon into another reservoir that would further damage the natural wonders of these United States.)

But I imagine you tell your dentist after he notes the cavities, gum disease, and other problems: "you keep telling me that if I don't start brushing and flossing I will lose all my teeth, but I haven't lost any teeth since I started brushing and flossing so you were lying when you told me that I would lose my teeth."