And the above is exactly why I won't go on any 'organised' rides, as much as one can appreciate the time & effort an individual goes into organising the rides and I would dearly love to go on one but frankly removing my choice to not wear a bit of polystyrene foam means I won't.
The excuse about insurers has being shown to be smoke & mirrors, there are insurers of cycling (events) that don't require helmet wearing as an obligatory std (CTC use them for starters) That no evidence can show the efficacy of helmet wearers compared to those sans helmet just further supports the stance that there is no risk..and in some cases actual incidents and/or worse injuries occur because of helmet being worn.
You may as well wear a helmet for getting out of bed, you've more chance of killing yourself that way from a head injury...
1958 Carlton Super Python
1990's Gitane VITUS GTI Triple Butted
1996 Raleigh Titanium Special Products Division
2007 Specialized Globe Pro
2007 Specialized Globe Expert Ultegra 6700
KTM Strada 6000 Carbon Dura Ace 9000