Saying that "thousands believe" does not make for a strong argument regardless. Thousands of people believe all kinds of things we collectively know aren't true (flat earth, didn't land on the moon, take your pick). I just lump loud pipers right in there with the flat earthers and anti-vaxers: people that believe what they want to believe regardless of the facts. You want to make a bunch of noise with your toy? Have at it, but don't try to pass it off as a safety feature.

I can easily throw an opposite opinion: besides riding motorcycle every single day, I drive car, and usually I notice motorcycles roar too late. Also, I had two occasions when drivers didn't notice sound of my motorbike (it's not quiet at all) and changed lanes right into me. So I prefer to assume every driver is deaf and ride that way.