I've been riding motorcycles since I was twelve and my father and uncles ride too. None of them wear helmets unless it's cold but I wear one every single time. At this point it's just uncomfortable for me to ride without one (a full face euro approved one by the way). Plus it hides the fact that I'm a woman.
So after long discussions on helmet laws, my opinion is that they should be mandatory for anyone under 18, or maybe 21. Kids do stupid things and we as a country tend to make laws for their safety. If you ride without a helmet as an adult, I reserve the right to tell you you're an idiot. As far as laws go, I understand why people feel that they shouldn't have to wear helmet but I think that the state should require extra insurance or something if you do. The idea would be to absorb some of the costs associated with having your head bashed in.
Realistically, DOT helmets are not safe enough to keep you alive in your average accident anyway. The DOT testing is simply not up to par. If it was, you wouldn't see half helmets on the market. People don't usually land on the top of their head in an accident (though, I have seen it happen). What is a half helmet going to do when your face flies into the back or front of a car? Or when you lowside and smash the base of your skull into the road? The reality is, even if you wear a DOT helmet, your chances of walking away from an accident are not great. That said, there are a lot of lives that have been saved by helmets. Mine included.
Edit: I wanted to add that the same things I mentioned above should always apply to scooters too. They are just as dangerous but I can count on one hand the number of times I've seen someone in gear on one.