Loud pipes, small *****
that is more like it
The main problem with the idea they are safer is you can't hear them in front of the bikes at all, only after they have passed you. Also low deep bass sounds don't carry direction well so you might know there is a poser harley guy within a 1/4 mile of you but not have any idea what direction he is. I hear people always trying to tell me they are safer by saying how they never get cut off anymore. I tell them I put 20k miles a year on my 85db quiet bike and never get cut off. Mainly because I know how to ride and watch out for other cars instead of trying to impress pedestrians with my cool bike and not watching the road.
I figure a loud horn is more useful so you can be a normal quiet person going down the road till you need to be loud then you can hit a button and make all kinds of higher pitched noise that everyone will know where it came from.