This is an example of the mentality that causes so much resentment towards motorcyclists.
First of all, the noise from open pipes is only when the rider is on the gas, and almost entirely behind the rider. Most hazards are in front of you: the Hurt Report stated over half of all multi vehicle crashes are left turners, and loud pipes are no help there.
Second, the noise might help you, but add a second loud bike, and everyone is worse off: no one else can hear a thing. And if you're on a normal bike, your presence is masked by a loud bike, or car, or truck.
Third, there are motorcycle safety studies that demonstrate the effectiveness of DRLs, high viz clothing, light colored helmets, full face helmets, ABS, and rider training. There are zero safety studies, anywhere, ever, that demonstrate that "loud" pipes enhance safety, for all the reasons stated above: directionality, sound pressure, etc. If you know of one, disabuse me.
Face it, the real reason for loyd pipes is vanity: "Look at meeee!"