Dedicated race cars are too few in number to really make a difference, so they don't worry about them.

This too is incorrect. If a vehicle is made with for street purposes, it can never have its emission devices removed. Even if it used as a dedicated race car

As you probably know, I was referring to custom built race cars, such as Indy or Nascar. But yes there is a very tiny set of cars that were once street cars that have been modified and now only race and never, ever, even for a minute, drive on the roads.

Maybe that might be worth regulating, but there aren't many actual race cars around.