To promote public awareness, I feel compelled to respond to the letter, "Loud motorcycles should be outlawed." Unlike cars with loud boom boxes, and unlike bored dogs that bark incessantly day and night, a motorcycle is loud for safety reasons. I'm not defending excessively loud motorcycles -- there are extremes -- but a quiet motorcycle is a dangerous thing.
I've recently started riding and I'm amazed at how often cars cut me off or pull out directly in front of me. This never happens when driving my car, so I have to assume it's a visibility phenomenon. To combat this tendency, many motorcyclists have chosen exhaust systems that make their motorcycles more audible to nearby drivers. I can attest to the fact that it makes a huge difference with regard to safety.
Again, I'm not defending excessively loud motorcycles. But if I'm forced to have a silent exhaust system, I may have to initiate a similar practice to the "headlights-on-all-the-time" safety requirement, and wire my horn "on" all the time. I think people would rather hear my exhaust.