I'm surprised that no one has trundled out the old chestnut that "loud pipes save lives" as some sort of justification. I suspect that is more anecdotal and less researched than, dare I say it, the pros and cons of cycle helmets.
What is probably more true is that loud pipes just annoy the hell out of most non motorcyclists and give bikers a bad name. I well remember blatting about on a Norton Commando in the seventies and enjoying the sound of it. It was pretty fruity sounding as it came from the factory, by no means quiet, but it was a low frequency mellow sound. It sounded great to me. This was also the era of Yamaha and Suzuki 2 stroke racing successes and of course road going expansion chambers, with their ear splitting high frequency crackling sound. What is music to some is just appalling noise to others. Yet the whiff of two stroke exhaust is something I still find very evocative to this day.
I suppose regarding the need to make noise as just a phase some people go through is not much consolation to those who have to suffer it, but it is easy to be judgemental and forget that many of us were there once. We have not sprung fully formed into life as intolerant old gits. We have gone through a process of experience and development to get there.