I am a Trauma/Critical Care RN studying to become a Hospitalist here shortly. I respect your choices to not wear helmets but on the flip side, I can't tell you how many TBI's I've dealt with in both Sxs's and SandRails because of a collision or rollover that have completely changed not on the lives of the driver but the whole family now dealing with caring for a TBI patient. I plan on wearing an Arai and will probably wear a Hans device or similar as Atlas (C1)/Axis(C2)/Bibasilar skull fractures in a harnessed seat are very real potentiality when your head goes slinging forward while your torso is locked in place not to mention the coup contracoup that yoru brain goes through. Just some food for thought.
~Andy