Do you actually bike? I ask because the statement "in the US, we'd do well to stop treating biking as a risky behavior" will come as a surprise to anybody who spends any amount of time in the saddle on US roads.
Do you live in sprawling suburbia? In a lot of major cities it's fairly safe, and it becomes safer the more people bike. What's stopping people is that it's perceived as being risky. I don't think we need to abolish helmets for that, but the perception that you will die of head trauma if you're riding a few blocks to the coffee shop is a bit much.
Suburbia definitely contributes to this problem with large multi-lane roads, hostile to both cyclists and pedestrians alike. A lot of their cycling projects also seem to be focused on multi-use paths, which are unlikely to bring up the count of commuter cyclists. They're poor to use as transportation or training options, which often leaves suburban drivers confused or frustrated when "there's a perfectly good path for you over there."
I don't own a car and my bike is my primary form of transportation. I live in San Francisco and bike almost every day.
So based on your experience biking in the most bike-friendly city in the nation, you're recommending that everyone in the U.S. go sans helmet? This seems, at best, naive.
I never said people should ride without helmets. And there are way more bike-friendly cities than SF.