Loud pipes argument is bullshit in my book, I've been riding for 5 years now and never had a traffic accident, defensive riding is the only way to be "safe" (you're never really safe on a bike, even a little gravel on the road can mean you end up in a coma), relying on other drivers having to notice you is a pointless gamble, just assume they aren't going to and drive accordingly. Also I notice people get startled by a loud bike approaching - and the last thing you want is to startle an insecure driver.