Excuse this, it will be a long post:
The reason why I said his idea of smashing rocks on peoples heads was stupid is because road users very rarely have to worry about falling rock. The commentor wouldnt accept that the majority of times a cyclist goes down that they consciously or unconsciously put their hands out to protect them from the fall. Looking at Le Tour, and I've watched for many years, how the majority of riders who go down suffer damage to their collar bones, wrists and shoulders, and then usually the legs and knees after. (Depending on how they fall). Smashing a paving slab on someones head doesnt match the angle of impact between cyclist head and tarmac either.
There are so, so many variables. No one study has been definitive and too many vested interests by researchers (helmet industry, dental industry, Headway, and ofcourse those who wish to remove us from the road - David Curry MP who looked into various stats to last year for his own ends it seems)
In no other situation where some one is a victim of an accident or collision do we bang on so much about "protection". People have to understand its still a personal choice - WE are the ones who suffer through an unclear choice - motorcycle helmets have heaps of physical research carried out to test them, as with car seatbelts. They've done the cadavers and crash test dummy analysis, they've tested and retested new designs.. We dont get that with cycle helmets.
When you hear of a work mate or friend having a crash in their car does everyone pipe up and say "well were you wearing a seat belt, or doing the limit?!"
Its rediculous. We as a nation are failing people by allowing non-cyclists to dictate to us what we wear because they are so afraid of their driving and that they might hit us. A far better solution is to deal with the bad road usage as I keep saying. Until people realise this we will continue to have these debates whether we ride or not.