I know, a little slow to respond. Was still enjoying the holiday.
My opinion - I think loud pipes are helpful, especially in keeping people attentive to your presence. Note, I did not say that I believe they necessarily save lives but they may. I find that to be difficult to prove either way because of other factors, including type of traffic you drive in, where you drive, etc. Also, I would think it is difficult to determine if the cause of a crash and subsequent fatality is related to the loudness of pipes. If someone with loud pipes dies in a motorcyle accident, does that mean the loud pipes did not help. Not necessarily. Also, if someone with quite pipes dies in a motorcycle accident does that mean if they had louder pipes they would be alive. No.
Reason I prefer loud pipes now - I rode my V-Rod with the stock pipes for a year, including about a 50 mile each way commute in Atlanta traffic. I had several cars pull over on me at 80 mph or so on GA400. I got out of the way each time because I am aware of Atlanta drivers and don't trust a single one of them. Because of this and the additional hp, I bought louder pipes (D&D 2 into 1 system). I have done the same commute more in the past 3 months then I did the entire first year and have yet to have anyone pull over on me. Additionally, all vehicles have maintained additional space between them and me, especially if they are on the phone, etc. Lastly, if I am gaining on someone they now tend to pull over out of the fast lane (an amazing thing in Atlanta) to let me pass because they DO hear me approaching. Note, that the D&D 2 into 1 system is very loud at rpm. Finally, the accidents such as someone pulling out in front of you will only be reduced by vigilance of the motorcycle rider. They ain't gonna see you, hear you, or care if they do sometimes. Don't trust any vehicle at a crossroads or similar situation.
Lastly - a comment about the AMA - I read the article related to loud pipes and their general position statement when they first put it out earlier this year. I was considering joining because I wanted someone that would protect the rights of all motorcyclists. That position statement helped me to decide that I would not join thier organization. I do realize that some people have an arrogant attitude about what they can and can't do; and somehow it is thier right to annoy the crap out of people around them. These people have the same attitude on many facets of life and ruin many things for everyone. However, I leave my house at 3:30 AM in the mornings so I can go to the gym. I have asked every neighbor if they have heard me leave. The answer for all is "no". I ride with the rpms as low as possible until I get out of my neighborhood and onto a major roadway. In other words, what I'm saying is that those with loud pipes - including me - can be respectful when in low noise areas but use the pipes to our advantage when surrounded by jerks like on Atlanta highways. To me it's the best of both worlds.
Y'all have a good day and remember this is just my opinion, do with it what you will. :2cents