Should certain modifications on your car be illegal?

This is a question that if you ask a car enthusiast you will most likely hear a resounding no. some people will answer yes for many various reason. One of the strongest arguments for making certain modifications illegal would be that a lot of these modifications require someone to play around with the cars emissions system. Many time f someone is doing a crazy build and decides to add a turbocharger to their car they will most of the time remove catalytic converters and mufflers in order to gain as much power as possible. This of course is bad for the environment but is it so bad that it would require banning. I don't think so. For one, there are not that many car enthusiasts in the U.S. which means that it is only a small handful of cars that would be polluting the air. Also a good majority of these cars are rarely driven. I have a friend who owns an RX-7 who has no catalytic converters on it. This car only sees a few hundred miles a year because he wont drive it in the winter and he doesn't drive it everyday to school and work. The environmental damage that his car does is very slim compared to some cars that are driven everyday. So like every other car enthusiast, if you ask me should certain modifications be illegal, you will hear a resounding no.