It is rather interesting, to me at least, that in this thread about safety the idea of 'loud pipes save lives' seems to some at least to be a given. While at the same time there is another thread about what many feel are overbearing and unjust laws being implemented in Germany to deal with the sound of motorcycles.
It would seem that either motorcyclists need to do a much better job of convincing the general public of the necessity of loud motorcycles, or have to admit that the aural assault that others perceive is indeed a problem. While I cannot deny that I have added aftermarket exhausts to most of the motorcycles I have owned I also have from time to time cringed at the sound of a straight piped Harley. I can say that the majority of my exhaust modifications have been done in conjunction with intake and tuning modifications in the pursuit of better performance, but I have to admit that in most cases I liked the sound.
I have read the scientific writings on how sound waves travel and how in most cases those hearing motorcycles, especially in traffic conditions, are hearing them after they have passed. That argument puts forth the case that those loud pipes don't help you when you are approaching another vehicle. But, from my experience sitting in plenty of cars and trucks in my lifetime, I have heard approaching motorcycles from behind many times. Of course, once they pass the sound is much louder.
I guess the takeaway is that increasing legislation is probably inevitable. Motorcyclists don't tend to be great lobbyists. So, in the future situational awareness is likely to have to play an even bigger role in motorcycle safety.