All I have is anecdotal but when i was doing my time on the bus and in the ER working on my EMT cert I witnessed far more rice burner casualties then Harleys. The severity tended to be worse with the rice burners as well. Had one impalement on a fence post with the Harley group (he lived but was pretty screwed up) but the majority was road rash and leg fractures from dropping the bikes on themselves (usually from inebreation).
The rice burner crowd though were into speed so their accidents were much worse. 5 fatalities in a year and a whole bunch of fractures etc. All the accidents that came in while I was in the ER were self inflicted. For some reason I wasn't working when the bikers came in who had been creamed by a car.
So there still is no definitive proof that loud motorcycles have any benefit what so ever.
Loud is a choice that some riders make in order to be more obnoxious. Why? Can't they find ways to be obnoxious to those who they know personally? Why do they have to be obnoxious to the world at large?
Well, I tried my best to point out that it makes a difference to me, and that I've experienced this in real life. I'm much more aware of where a motorcycle is in traffic if I can hear it rather than not. But it's ok if you want to go on ignoring that, but I call that proof.
And loud pipes, in your opinion, are obnoxious. Well in MY opinion, it's cool and I like it, and we're both entitled to our own opinions. Now do I believe someone with loud pipes should be blaring past homes in a residential area at 2 in the morning waking people up? Not only no but HELL no. They should be ticketed, but it would be no different whether it was a bike, a car, a truck or a UFO. Loud is loud.