Joseph Stromberg crunches data from around the world about bicycle safety and the question of whether helmets should be required for bikers. The title of the article "Stop Making People Wear Helmets" makes the politics of the article clear, but here's the crux of Stromberg's argument: "Most importantly, requiring helmets deters many normal people from biking in the first place — in Australia, bike commuting rates plummeted when mandatory helmet laws went into effect. And, when there are fewer bikes on the road overall, biking becomes more dangerous."
Stromberg backs this up this claim with a number of data-backed arguments—including the relative danger of biking compare to walking and driving, the effectiveness of helmets in reducing injuries, and the surprising point that helmets might, in fact, make accidents more likely (although that final point is hard to prove scientifically).
A final, thought-provoking point: "Let's stop thinking of helmets as a critical protection against the risky activity of biking. Let's start thinking of biking as a normal, safe activity, like walking — and helmets as an optional accessory for people who are really into it."