These questions almost always bring out the debate gene in all of us. I also agree you have a right to take the risk of not wearing a helmet. There is nothing magic about a helmet and it may not save your life. But if you read the many posts here of people who have been riding for quite some time and even with that much experience still managed to crash and take a goodly portion out of a perfectly good helmet you can see it could at the very least save you some cosmetic damage to your head.

The real question would be why wouldn't someone wear a helmet? You don't have to have a real expensive one so it isn't cost. If it provided "any" protection to keep you from losing part of your skin or hair it would seem like it is worth it. When you get that slow leak that causes your tire to roll off the rim in a corner and you slide even six feet on pavement just think of sand paper sliding on your head and what it would do. Pavement is much courser than sand paper.

No reason to add my stories about pace line crashes and just plain falls. Lets just say if I am going to fall, and if you ride you will fall, I would rather have something between me and my sliding head that sun tan lotion.