I'm of the opinion that everyone should have the chance to choose whether they wear one or not. However having said that I nearly always to wear one but can't say if they save lives or not. What I can say is that I recently had an off and suffered a broken collar bone and had some nasty abrasions on my elbow, knee, leg and ankle. When in the hospital the nurse noticed that I some red marks on the side of my head which turned out to be from the padding inside the helmet. The doctor ordered a MRI scan which was taken and showed no problems. When we later inspected the actual helmet it had some scratching on the outer coloured covering and the 'foam structure' was cracked in two locations from the bottom rim to almost the crown of the helmet.
I can't say it saved my life and am not trying to, but I can say that it saved a lot of bruising and road rash to the side of my head and I'm very happy I was wearing the helmet!!!!!!!!!!!!!!!!!!!!!!!!!!