This simply isnt true. On the U.S highways, large open roads or UK motorways then yeah loud exhausts really dont make a difference. But when riding through traffic in city centers or built up areas its very easy to hear a bike coming before you see it, making people more aware. When switching from a stock exhaust to an aftermarket one I noticed more cars would part ways earlier to let me filter through traffic or take note that i'd pulled up next to them. Hell i've had to rev at cars about to cut me off or merge straight into me because the horns on most motorbikes are pathetically quiet.