Whoa, whoa, whoa. I did NOT say that helmets are no use.

I was referring specifically to the situation you describe, where your helmet not only doesn't stay on your head, but it interferes with your vision.

While I strongly reject the concept that lives can be saved, most fates are much, much worse than death. A helmet has saved me from one, myself. Before you ride without a well-fitting helmet, think about who you would like to wipe your butt and feed you pablum for the rest of your life, and ask them whether that's going to be okay with them.

It's true that once you get over 50 mph or so, internal and/or spinal cord injuries are likely to be much more severe and disabling than anything a helmet could prevent. When MOST of your time riding is spent above 50 mph, then maybe you should graduate to a motorsports helmet.