Albeit unintentionally; it was the most obvious practical objection that came to mind.

I believe how acceptable ones vision is in sunglasses in a car is debated, though I wouldn't debate it. Yet I would say that it's less than it would be without them (except under particular conditions, e.g. polarized sunglasses when there's a lot of unpolarized light). That is, it's ACCEPTABLE, but I do think it's DIMINISHED, however marginally. Helmet visors, however, face other challenges; sunglasses don't get rain, mud, oil and bugs on them, which is why, as I'm certain is also true of your helmet visor, they don't have wipers or washer bottles. Meanwhile, DESIGNING something to not restrict peripheral vision is not PREVENTING it from doing so, and even if you do design a helmet with zero peripheral vision resriction it's kind of a Catch 22: The less it restricts your vision, the less of your head it covers and therefore protects, and the less protection it provides the less basis there is for this whole discussion.

You know better than I, naturally, but the helmets I've seen designed to facilitate hearing (and that such helmets exist indicates a strong belief that, at least in some circumstances, other helmets DO impair hearing) merely had holes on each side. Maybe an inch and a half across, does that "sound" right? Of course, sound reaches our ears from all directions, not just through narrow holes right next to them (after all, our ears themselves are structured to focus sound so that it enters the auditory canal even when not traveling directly toward it). If you do mean helmets fully open at the ears we're back to the above Catch 22: The helmets protection doesn't just stop where riders vision begins, it stops where their ears do.

I'm willing to take your word for it, though I still think it's debatable; you ride and I don't so I can only offer second hand anecdotes and sound speculations that nonetheless aren't necessarily valid. That said, I think I have at least demonstrated why a helmet visor is more than just a pair of sunglasses attached to your helmet.

No argument there; it's one of many reasons I wouldn't touch a bike with a 10' pole. However, wearing a helmet doesn't solve that problem, and I feel fairly confident you'd still rather try to avoid than endure an accident even knowing you have less traction and more concern about center of gravity than you would in a small car. Small and quick carries different liabilities than big and thick, but it seems pretty obvious which is more easily augmented in a motorcyle.