the fact that this thread exists makes me upset, but i feel like i have an important contribution to make.
this past august i feel skateboarding (yeah not a bike but i fell regardless) and tried to roll it out instead of going on my face. i ended up cracking the base of my skull and spent a week in the ICU with subdural hematoma. the ONLY reason i'm still alive is because i cracked the absolute thickest part of my skull. a friend of mine fell the same way skateboarding in December, received the same injury, and is now dead.
Don't give me any "well i know what i'm doing" or "it impairs my senses". thats not the issue at hand. if you fall on your head, a helmet will quite possibly save your life. end of discussion. if anyone would life to discuss this further i'd be happy to argue the helmet side all day.