Ladies and germs, I am AGAINST MANDATORY HELMET LAWS. I am against them for the same reason I am against a number of other societal compulsions related to personal behavior.
I watch the actual scientific debate about helmets with interest. With equal interest do I view the squalling of the most ardent opponents of the brain bucket.
At the very least, your average helmet will blunt the impact of the average thrown beer bottle hurled by some redneck humorist with a better than average pitching arm.
I've never cycled outside the United States. Some places have been better than others. A lot depends on your goal for cycling. I don't like to do it as a destination activity -- something I go to do in a closed venue and then return home, usually by automobile. Other people will only do it that way. Every different cycling group perceives it in a different way.
Back in the 1990s I even remember a letter to a bicycle magazine, allegedly submitted by a mountain biker, promising to run road cyclists into the ditch if he saw any, because he believed mountain biking was the only form anyone should do. Here was a cyclist who believed roads are for cars, who threatened bodily harm to any Lycra faggot roadies who slowed him down on his hurtling journey to his favorite trail. Since these letters are as hard to verify as an anonymous blog comment, who knows if it was true. It got published.
This was right in line with what Brock Yates was saying at the time. Bikes are great. Keep them out of the way of progress.
Helmet choice depends on an individual rider's perception of the potential dangers of each riding venue. I guarantee that cycling in traffic in the United States significantly increases the chance you will have an openly hostile encounter. Just as military helmets wont stop a bullet or prevent a traumatic brain injury from an IED, so will a cycle helmet be of little use against the weapons leveled by road-raging motorists. But in the multi-variable environment of many streets, it might come in handy.
Motorists need not be hostile to be dangerous. They might simply be ignorant and impatient. You're running with a herd of nearly blind beasts with thick hides. Many of them have no thought for the little scampering things that insist on sharing the stampede trail with them. Others will swerve so far as to endanger their own kind, further increasing the anger of a few of them against the little scampering things. What are these little scampering things?! I want to stomp one!
Experienced cyclists using either official Effective techniques or whatever techniques they have individually developed will have far fewer accidents than cyclists that blunder around carelessly. On the other hand, maybe you just get the chop when your number comes up. Dance naked through live machine gun fire in the morning, slip and shatter your skull in the shower that night. We only think we know what we know.
I think, therefore I am mistaken?
If we all weren't already nuts, this would drive us crazy.