If it's so inherently dangerous to ride a Harley that their loudness is required in order to achieve an acceptable level of safety, then no one should be riding them, period.

If non-Harley motorcycles with reasonable noise levels are insufficiently safe because they're so quiet, then no one should be riding motorcycles at all.

I don't agree with either of these perspectives, but whenever anyone makes the "loud pipes save lives" argument, this is what they are saying. It might look good on a bumper sticker but it doesn't make sense. It's no different than suggesting that all pedestrians walk around screaming gibberish as loudly as possible at all times, to reduce their chances of getting hit by bicycles.

If I really believed that I needed to ride a Harley in order to ride safely, I would stop riding altogether. It's not worth annoying hundreds of people every single day just to indulge myself in this one thing. I would find a different hobby.