This policy is fiendishly clever, because it seeks to protect us from dangers that will actually increase as a result of the policy, and places those who already behave virtuously (in the view of the policymakers) in greater danger than they were before.
We know roughly three things about cycle helmets with a fair degree of certainty (there is not that much research):
2. making cycle helmets compulsory does not reduce the overall number of cycling injuries or fatalities
If we add a further piece of knowledge
then we get this:
The NI Assembly is placing cyclists in greater danger, although there is a small chance they will slightly better protected against this danger. As long as they didn't wear a helmet in the first place, in which case this will be less safe than they were before.
I guess as things go at the moment, this is not the gravest example of policy stupidity around at the moment, but it's still worth stopping: sign the petition here!
NB By the way, I'm a helmet wearer.