It should be same as seatbelt and airbag laws, with police being able to pull you over and issue tickets. Enforced with minor slaps on the hand.
The harsh truth most citizens especially us Americans don't want to hear is that the average adult barely qualifies as sentient and no more able to accept accountability for their own actions than the children they pop out.
People want the freedom to do whatever they want and rant about liberties and rights. But when faced with consequences of their actions they tantrum about how its something elses fault, blame the system for not forcing their hand, and squirm their way out of responsibility at first opportunity while trying to sue sue sue.
Alternatively to to ticketing, you can ride without a helmet, but you must be exempt from public Medicare type insurance when your dumbass inevitably splatters your brains on a highway. You want the thrill? Fine. Accept resonsibility and pay up the price when it bites you, if you still can.