I briefly had one because a number of organisers of sportives started making them compulsory, but couldn't stand the things and instead stopped riding events where one was required. Interestingly enough, the last sportive I road, sometime around 2010 Myself and one other were the only ones without helmets, he because he had forgotten his and myself because I chose not to - and guess what, In was thew only rider to have an off. Climbing a slow grind of a hill on an unclassified road I put my front wheel on a patch of mud, went 90 degrees across the road and fell on my side down the hill, a classic case one would think where a helmet would come in useful. Except My head never made contact with the ground, as is usual in such falls I took the impact from my shoulder downwards, hard enough to make me abandon the ride within a few miles of getting back on the bike.
I have no doubt that if I had been wearing a helmet the increased bulk and weight would have caused it to touch down and shatter, giving me the perfect excuse to come on here and post a "Helmet saved my life" thread. I've been cycling and racing long enough to have seen that deaths from head injuries alone have always been very rare among cyclists, I don't know of any myself though I have known of a few deaths of riders I competed with. Go back to pre compulsion in pro racing and see how many head injury deaths there were among the riders and you'll struggle to make a statistic that would amount to a tenth of a percent, and these guys crash regularly as an occupational hazard.