In '70 - I got T-boned by a woman gunning it from a stop sign, didn't see me - I was wearing a bright yellow rain poncho, it was about noon. As her bumper hit me I looked down and saw my boot and ankle being crushed between the bumper and the transmission case. I flew over the handlebars through the air into oncoming traffic, rolled a few times after I hit, took me several minutes to crawl back and turn the bike off, the engine was at WOT. Spent several weeks in the hospital. Ankle is still a problem to this day. I'm pretty sure if I had not had the helmet on the ankle would have been buried with 1970, along with the rest of me.
I think anyone who rides without one should be required sign away any right to compensation for head injuries to ensure that those of us that do wear helmets don't have to pay higher rates. Go ahead, take the risk, just don't make me pay for YOUR poor decision.