According to a leading neurosurgeon bike helmets a to flimsy to really protect the head/brain.
Cycle helmets are useless, says brain surgeon - Telegraph
This I can agree with.......to a point.
The problem is, as I see it, is weight and cooling that can't be had with heavier materials. All other type of helmets use plastics ,and padding, that had pounds, not ounces, to the rider to supply the energy to move. I guess it comes down to "thinking" you have protection when you really don't know for sure.