I would advise you wear as much protection as you feel you need. 3 years of karate has definitely paid dividends for me as it has simply taught me how to fall better and tuck/roll when possible. So of my 3 nosedives (1 at 24mph like a bozo in a hurry to get home at 3am), my head has never touched the ground.
Coming from a motorcycle safety enthusiast back ground they say "Don't dress for the ride, dress for the fall", but damn that wind feels good in the hair. I wear my motorcycle jacket every day though and that has certainly saved me some skin.
I believe people should be free to live their life with whatever degree of apparent danger they feel comfortable with sans criticism.