Remember kids... always wear a helmet. (The almighty bikeradar helmet thread)

Leaving aside the question of whether it is rational to wear a helmet for safety reasons, could it be rational to wear one to ensure that you or your family don't ever have the question of 'what if?' or the lingering feeling of 'I wish I'd pursuaded him to wear one'.
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Only a 'what if?' to some people. If a member of my family had a head on with a van I would be asking a few what if's but none about wearing a helmet or not.