Nope. Wear a helmet ONLY if you choose to do so. I encourage helmet wear on bicycles and motorcycles, but YOU have the right to decide whether to do so, while understanding that you accept whatever consequences you might face. It doesn't bother me in the slightest when someone in the group rides without a helmet.

Likewise seat belts. If you don't wear them, that's YOUR choice, unless you're in MY car (and I'm therefore responsible for your safety).