As a lifelong motorcyclist I'd say this is twaddle, there can be no justification for polluting people's lives with noise. Whenever I got a new bike I used to fit a pair of Fiamm diaphram horns and I had reason to be grateful for them quite a few times but that was only momentary noise, not neighbour-disturbing and ear bashing noise.
And yes, how would a driver that's about to pull out on you hear your exhausts?
Well i think you're talking twaddle, its my experience that louder exhausts does make bikers more noticeable to other motorists. This is 40 years of experience of being a car driver and a motorcycle rider.
You may disagree with me on this, but you wont change my mind about it.