The US is absurd: you don't have to wear a helmet on a motorbike, but you need one on a pedal bike ?!?
There's no national law in the US regarding helmets. It's a state-by-state (and in some cases, city) issue, and most state's don't require that adults wear helmets. That said, I don't know where you get off saying "The US is absurd" when the thing you're calling absurd doesn't exist.