My friend had an accident on one of them and he had on a helmet, but he had all sorts of head injuries anyway because the helmet came off ...
Then he didn't have a helmet on, did he? I'm not exaggerating when I say that a helmet isn't likely to come off without taking the head with it. If your friend's came off, he wasn't wearing it properly. Which means he wore it because the law said he had to, and went out of his way to comply with the letter but not the spirit of the law. Is that the kind of attitude that would lead to reckless riding? You betchya.
The police reported that the strap had broken, so they didn't know if it broke when he hit the hood of the car or broke when he hit the pavement. It's possible he was wearing it properly and it was worn out and he was unaware of it, which was what the police report said.
Besides that, you're basing your conclusion -- "Those things are dangerous!" -- on a sample size of one. Well I know someone who died in a car accident. Are you going to stop driving? I didn't think so.
I'm not really basing it on one incident. I know of many many incidents, some where the person died, (friends of mine), some where they were disabled, that had motorcycle accidents. I'm not saying cars aren't dangerous, because any moving vehicle on the road is dangerous. It's just that cars offer a little more protection (airbags, seats and sides and doors to make you less likely to become a human projectile flying through the air, etc. Doesn't mean it can't happen, my own father was flung through the windshield of his old Chevy years and years ago, so it can happen. It's just a little less likely to happen in a car or other vehicle than a motorcycle, unless you're riding in the bed of a pickup truck.
For that matter, even walking is dangerous, but that doesn't mean we should all hole up in our homes and become hermits. ;)
Brenda