The answer is: to argue.
In the passage above, the author is clearly making an argument in favor of using helmets, regardless of the age of the bike´s driver and in the face of so many accidents (300,000). You can clearly see this is indeed the purpose of the passage since the author is literally claiming to provide a reason for such an action, and the author supports this claim by providing proofs, which are that a helmet protects the body in the event of an accident.
