I don't see what the Doppler effect has to do with any of this. And as for Japanese bikes and BMW's, you have a point with the Beemers. But that's probably because the riders are all against loud bikes, and says nothing of the relative safety. As for riders of Japanese pseudo-race bikes, well, I've heard some of them that would put any loud H-D to shame.

I had mufflers on a Shovel, and an old guy in a Caprice convinced me that I needed them gone. He didn't say a word; instead, he drifted aimlessly into my lane, expecting to occupy the same space as me. Fortunately the road ahead was clear and I could open it up and get in front of him.

The bike was pretty loud without the mufflers, but it wasn't really very bad if I kept off the gas. And I rode pretty slowly through residential neighborhoods. But boy, when I opened that thing up, you couldn't miss it. It would set car alarms off with ease.