A new re-analysis of the data published at the Conversation shows there’s a good case for keeping helmet laws.
I don't know enough about the topic to have an authoritative opinion but it strikes me that this issue is reminiscent of many of the trade-offs that have to be considered in HIAs. Namely, moderate benefits to a larger group of people being traded off against severe impacts for a small group.
The current debate around helmet laws has focused on historical analyses of policy impacts, but there's been relatively little discussion about the role that values should play in guiding decision-making. A precautionary approach might suggest that you need to do everything you can to reduce the incidence of brain and other injuries (a focus on severity). A comparative risk approach might weigh up the scale and degree of benefits to a broader group against the negative impacts on a smaller group(a focus on magnitude).
We can't pretend this sort of decision-making doesn't involve values.