I don't wish to debate, simply stating my opinion:

Why would you not wear a helmet? Despite the fact that over a number of wrecks, I have never had a wreck on either my recumbent trike or DF that resulted in a potential head injury, I still wear a helmet, even to go a few blocks to the grocery store. The way I see it, just because I've been fortunate so far, there are no guarantees in life. And regardless of the fact that a head injury is highly unlikely on a bent, I figure "why chance it?" and I afford my noggin all the protection I can. As far as I'm concerned, that's just good policy, seeing as how you can't really live without your brain.