I know
Very much depends on the type of roads, riders and drivers. Not many people wear them in Amsterdam (although more nowadays) but the roads are set up to provide cyclists with priority
In my opinion though they don't do any harm
Any argument for wearing a helmet on a bike, is actually a stronger argument if the same logic is applied to pedestrians, and even car drivers. Would you advocate pedestrians wear helmets or in a car?
According to the experts, they are only of use at speeds and impact forces where head injuries wouldn't occur anyway. They can increase the risk of injury directly, through strap or rotation, and they increase the overall false perception that cycling is dangerous, reducing the numbers of cyclists. They give a false sense of safety, increasing risk taking by the wearer, and also cause drivers to go nearer, and increase the risk of injury.
Boxing withdrew head guards, as the net result was more head injuries.
If the money spent on helmets had been put into meaningful road sharing awareness, then safety would be far better served than through wearing a plastic cup.
EDIT: Just to add, another danger in making claims for helmets that the facts can't back up, is that it supports the claims for compulsory wearing, which have shown to reduce cycling as it gives the false perception that it is dangerous and increase the accident rate as it fools cyclists and drivers in to thinking they are protected.
