The main problem with all noise ordinances, other than the obvious discrimination when singling out one particular type of vehicle, is that you need a scientifically valid method to measure the sound output if you expect the ordinance to survive even a half-azzed attack in court. And so far no one seems to be too interested in spending the kind of money it would take to set up a valid test site, then figure out how to get the offending vehicle to the test site and who would have to pay for the entire process. The reason many places have embraced the idea of requiring the stock exhaust with the original manufacturer's stamped certification on the parts is that it removes all the onus of actual sound level testing. I don't think your average legislator understands the ease with which a person can modify the guts of the mufflers to increase sound levels while keeping that nice EPA certification stamp on the muffler shell, but there again I'm not so sure they really care about the actual sound level anyway. It's all about appearing to be responsive to those complaining about that sorry bunch of azzholes who do strafing runs past their house at 2:00 am every Saturday. And make no mistake, the complaints aren't created by folks riding normally on bikes with slightly louder than stock mufflers. They are created by the jerks who run straight pipes or gutted mufflers and purposely rev the engines and wind them out, preferably in large groups to maximize the irritation factor. In other words, a bunch of juvenile delinquent types who never outgrew their need for attention.
Treat the non-riding population with a little respect, and you might be surprised at how this stuff fades away. In the meantime, don't throw away those stock pipes, keep them stashed in the garage or basement so you won't have to buy them later for twice the price.
Jerry