As a long time motorcyclist from a State that had no helmet law, I can tell you that if you really do your homework on this issue there is not one clear winner in general. If you are the kind of rider that is really cautious, drives no faster than the speed limit and follows all the rules, you may get run over by some car/truck driver who does none of the above.
Without a helmet, I can hear and see my
opponents much better, and by traveling faster than everyone else I never have to worry about what's behind me. Also, if you really look at the statistics, helmet use increases vertebra trauma (paralysis) because when the whiplash thing happens there is all that extra weight.
I have been down a number of times, but not as many times as if I always wore a helmet.
Just like diving, there are people riding who should not be riding.
They should wear a helmet. If you regularly stop at yield signs when there
can not be any traffic in the lane you are yielding to, you do not have the situational awareness to safely operate a motorcycle.
:focus:
If you regularly find yourself with not enough gas to make a proper ascent, you do not have the situational awareness to safely dive.