Loud pipes save lives. You've surely read this a thousand times on t-shirts, stickers, hats, and even tattoos. If you didn't know, this mantra demonstrates the idea that having a noisy exhaust will alert other motor vehicles of your presence, which will prevent accidents. My opinion is that this is mostly untrue. I know that this will be viewed as blasphemy to many bikers reading this and I may have had the same view in the past, but it has been shown that bright reflective clothing, good headlights, and an effective horn are greater deterrents for traffic accidents than loud pipes.
The thing about exhaust sound is that it's largely heard behind the motorcycle and you would much rather alert vehicles in front of you to your presence. I know motorcycles have been rear ended, but that makes up a tiny percentage of multi-vehicle motorcycle accidents. If your truly worried about saving lives, loud pipes should be near the bottom of the list of your concerns.
Now that the lecture is out of the way, I'd like to point out that I still like loud pipes! How about we say, "loud pipes kick ass?" The patch below is also one of my favorite when it comes to showing love for loud pipes. Let's just admit that we have a loud exhaust because we think that it's cool. At least that'd be honest!
"You got loud pipes, but you ain't sayin nothing!" - Junior in the motion picture Torque