I only need to look at Gary Busey to see why a helmet is important. If you hit a rig at 50, it won't make a differece, what does is keep a minor spill a minor spill. Doesn't take much of a hit in the right spot to turn your melon into jello.
I'll put it this way. At 14 I was hit by a car while riding a bicycle. Banged up pretty good hip, arm, shoulder issues, but the worst was cracking my head on the windshield. Had I been wearing a helmet I would have been fine, but those were the days before anyone wore a helmet to ride a bike. It took me years to get back to normal (whatever that is) from the head trauma. Don't get me wrong, I wasn't in horrible shape or anything, but lost some hearing, dizzy spells, blackouts for years. Had I had a helmet on I would have been fine.
So I chose to wear one ALWAYS, usually a full face. But I agree it should be the choice of the rider. They say it's b/c of a drain on the Healthcare system to treat these guys who wreck without helmets and no insurance. For some reason I can't believe that's the biggest drain on the healthcare system...