The premise that “loud pipes save lives” is a myth. There is no evidence whatsoever that it’s true.
The nation’s largest organization of motorcyclists, the American Motorcyclist Association, holds a long declared position against excessive noise.
AMA Position Statements: Excessive Motorcycle Noise
“The American Motorcyclist Association, established in 1924, has maintained a position of strong opposition to excessive motorcycle noise throughout its history. It has funded information and public relations campaigns in support of quiet motorcycle use and was the first motorsports sanctioning body in the world to regulate and reduce the sound level of racing vehicles.”
There are others who have organized their thoughts on this subject:
Loud Pipes Save Lives or The Madness Behind the Myth
“So I decided that perhaps the best approach would be to do some digging and see what I could find in the way of supporting facts, both pro and con. Perhaps I was wrong and they really do save lives, seemed doubtful, but I've always considered myself as someone who is willing to keep an open mind until the facts are in. In doing my research on the subject I found many opinions but very little in the way of hard facts on the issue of "do loud pipes save lives?" In the end I could not find a single "fact" that supports the idea, but I did find a number of opinions to support it, opinions that were, as far as I could see, weakly masqueraded as "facts". To be fair, neither could I find any facts in support of the idea they don't. What I did find was numerous reasons why (overly) loud pipes can be detrimental to motorcycling as a whole. Here's a synopsis of what I found.”
MC Safety--March 2001
“In light of the negative effect that loud pipes have on motorcyclists' image, I simply can't buy the "loud pipes save lives" argument. It's especially hollow coming from someone who disregards traffic laws, doesn't use a riding strategy, has never taken rider training, doesn't wear a helmet, or doesn't wear protective gear. Do all these things as a rule, because you're honestly trying to reduce your risks, and the argument might hold water. It's possible that a loud pipe may, in some unlikely combination of events, save your life, but it's doubtful. There are far more effective ways to reduce your risks. The crux of it is that, until you've covered absolutely every other base, that worn-our battle cry is just a way to rationalize your flagrant self-indulgence. You'll not be fooling anybody but yourself.”
To me, it seems that the entire issue is the behavior of ignorant irresponsible people and has nothing to do at all with motorcycles.