you're completely right.
so is eheath about beating a X horse
life is unpredictable. helmets can be lifesaving even if you have an accident that might not be your fault whatsoever (maybe you were just in the wrong place at the wrong time). preaching for helmet advocacy won't get anywhere, unfortunately, until people/ organizations take a different approach. park city, for example, did so by requiring their riders to wear helmets when filming for the IRPC edits this season. now the skiers/ snowboarders probably weren't very happy about this and that's why, as right as your are, it will always come down to personal choice.
you don't wear a helmet for the majority of activities you do in life (eating, running, driving, playing frisbee, dancing, swimming, drinking....), so putting one on for skiing seems unnatural. now maybe this activity is inherently more dangerous than other (more casual) life activities, but for skiing to be natural and relaxed, helmets often don't factor in the mix.
this discussion could go on, and on, and on, and on
there are sooooo many valid points from both sides and honestly, you're right. everyone should wear a helmet for their own safety and out of respect for friends and family.. but does that mean all skateboarders should wear a helmet too, or that you should never ride a skateboard, bike, snowboard, pair of skis without a helmet on... maybe. but we're a long ways from getting there so for now let's focus on safety as a whole, on or off the mountain, regardless of helmet usage.