I think for this discussion to ever get worked out rather than people just get huffy and state their grand theory rather than debate the individual points of how a helmet is used and what it can do for a rider is to start from the bottom of the argument.

So start at the question of, does a helmet prevent a head injury when you hit your head?

Here's where it could lead from there.

Yes, ok so does this "gyroscopic wingwangs" cause people to hit their head more?

Does the risk increase factor actually exist? In what kind of people?

What causes most crashes that involve head injuries?

Are these common crashes?

etc etc.