There's just no reason for bikes to be loud. Some of the fools that ride noisy bikes will try to claim that it's a safety issue because motorcycles are harder to see on the road since they are smaller than cars. This argument is completely bogus. There has never been a conclusive study that being noisier equates to being safer. It's simply more annoying. Even Motorcycle Cruiser Magazine debunks this myth.
Myth 2: Loud Pipes Save Lives
Yeah, there are a few situations—like where you are right next to a driver with his window down who is about the to change lanes—where full-time noise-makers might help a driver notice you, but all that noise directed rearward doesn't do much in the most common and much more dangerous conflict where a car turns in front of you. Maybe it's the fatigue caused by the noise, maybe it's the attitudes of riders who insist on making annoying noise, or perhaps loud bikes annoy enough drivers to make them aggressive. Whatever the reason, the research shows that bikes with modified exhaust systems crash more frequently than those with stock pipes. If you really want to save lives, turn to a loud jacket or a bright helmet color, which have been proven to do the job. Or install a louder horn. Otherwise, just shut up.
So write your congressman, beat down a Harley rider or simply verbally abuse him, just do whatever it takes to get these nuisances off the road. There's no point annoying the majority of the population so that some losers can compensate for their small genitalia.