I not passing judgement at all but only relating what I found out when I was looking to use a helmet light.
Apparently a sharper pointy object like a light is far more likely to pierce a helmet than say hitting your head on a pavement or heaven forbid a car but whatever the object something that's flatter, the impact is spread, probably causing less damage than something that concentrates it in one area ... granted you may fall off your bike and hit the sharp edge of a fence post or other pointy object but the most likely impact will probably be the ground ... don't ask me how I know
It's widely believed that the Schumachers' injury's were worsened because he was wearing a Go pro on his helmet.
As I say I'm not casting any judgement but simply passing on what I found out when I was going to get one but in the end decided against it.