I live in NH, close to the ME border. Almost all my riding is done in these 2 states, and neither have a helmet law. For me, if I wear one or not is based on what I'm doing. For a slow easy ride, not doing anything I wouldn't do on my pedal bike, I sometimes don't. If I'm going to be dealing with traffic, picking up the clip, etc. then I wear one. I believe it's a personal choice, like seat belts, and people should be left to make thier own choices. If I'm running to the store in a 25MPH zone on a nice night and don't feel like gearing up, why should I have to? I'd ride the same speeds in the same place on a pedal bike, and I wouldn't wear one for that. It's all risk assessment to me. If I calculate there to be a reasonable amount of risk, I gear up. That's racing boots, jeans or riding pants, jacket, gloves, and helmet. If I'm going for a slow putter to shoot a game of pool or hit a store in town at mild speeds on slow roads, it's not worth it to me to gear up.
If you want to wear one, by all means, you should. If not, that's your choice, at least in some states. I accept the danger that comes with all choices I make, and that includes getting on a motorcycle, or in a car, regardless of the safety precautions taken.