That it can be extremely useful in some situations does not mean that it is overrated. I've been in a high speed bike accident where I was knocked out despite wearing a helmet (ironically, I'd just started wearing a helmet the month before because my cousin was put in a coma for a month after a high speed crash without one).

I still think they are way overrated. Nothing even comes close to contributing to safety in a car or bike like an attentive pilot. But in the US, we only focus on mechanical safety features.

I buy the best ventilated helmets I can find, but I still hate them. Wearing a beer cooler on your head on a steep climb or extended distances in heat contributes to overheating. However, I'll be danged if I'm going to fly down a twisty road at more than 40mph without one.

Most people ride at such slow speeds that they contribute far less value. Sure, it is possible to get hit by a car or fall at 15mph and cause severe head injury, but I can do that running, walking down the stairs, falling off a roof, or taking a shower for that matter. However, the vast majority of those accidents -- including those related to mechanical failure -- can be avoided if the rider isn't clueless.

Wherever I ride, I am blown away by how little awareness people have of their surroundings and equipment. This is particularly true in town where cyclists often make no effort to be visible and act as if huge chunks of steel that could crush them aren't even there.

Awareness of surroundings, proper riding technique, and ensuring a bike is properly adjusted and maintained (headsets nice and tight, tires and brakes in good condition, etc) contribute far more to safety than the helmet.

The helmet is but a single method for enhancing safety. If you wear one and do all of the above wrong, people will think you are safe. Get all the other stuff right and skip the helmet, they'll think you're nuts. This sort of logic belongs in the same category as thinking that riding on the sidewalk is safer.