For sure helmets have there place and can offer excellent protection, no question about that.
If you are kiting, and are likely to hit the beach, rocks, other people, your own board, or the Whitfords sea rescue boat, its a no brainer.
However IMHO there is more to it than that. Most of the reasons for wearing a helmet focus around being knocked out, and if you hit something hard or sharp, then for sure it will help, but it will only help, it will not always prevent an injury, and certainly wont always prevent a KO.
I've knocked myself out twice now, not something I'm proud of, but it happened. Both times were from hitting the water too hard and fast, I didn't hit anything else.
From what I understand, I knocked myself out because my head was stopped quickly by the water and my tiny brain hit the inside of by skull too hard and coursed the trauma. Interestingly enough, one time I was wearing a helmet and one time I wasn't. The time I was wearing the helmet, took longer to recover from and I had more whip lash. So I suppose there is the argument that my head stopped quicker after impacting the water with a helmet, coursing more trauma to my tiny brain and neck muscles.
At the end of the day, to each their own on this one, we are all responsible for our own actions, and if a bit of plastic on Plummets head gives him that bit of extra confidence to try something new, it got to be a good thing.

However as I'm sure Phillip Hughes family will testify, helmets will not always give you the protection they should.