Biking in Amsterdam is leagues safer then biking in most places in the US, though. The risks are different. Helmets aren't as important if most of your crashes are going to be with another low-speed, mostly-soft bodied cyclist. Traffic and pedestrians are pretty separated and you have your own lanes to cycle in. I'm also pretty sure that a lot of biking is convenient: The local grocery store is just a short bike ride but it'd take 15 minutes by car.
Most biking in the US is biking shared with cars. You probably won't have a bike lane. Most likely, you aren't commuting or going to the grocery store - the grocery store might take 15 minutes of driving but 30 minutes of biking - if you can even go the most direct route legally. Longer biking sessions generally means more risk. I'll take the helmet in places that I must defend myself against automobiles on an unsafe path.
Most biking in the US is biking shared with cars. You probably won't have a bike lane. Most likely, you aren't commuting or going to the grocery store - the grocery store might take 15 minutes of driving but 30 minutes of biking - if you can even go the most direct route legally. Longer biking sessions generally means more risk. I'll take the helmet in places that I must defend myself against automobiles on an unsafe path.