Exactly this.
When you've been told as a child, from medical professionals, that one more severe knock to the back of the head could kill you, it's enough to put the fear in you.
Granted my skull will have re-strengthened by now but I'm still gonna wear it, even if it only increases my chances 10%. On a scale of prayer to guarantee, I'll take 10% any day of the week and if it gives me confidence then I'm all for it.
The CQB site I play at has a leaky roof which leaves puddles of water full of slimey green algae on a completely concrete floor. I have boots that can deal with oil, ice, BB's etc but algae bests them easily.
Not to mention the many trip hazards from building debris, other people and my own feet and the multiple stairwells.
Yeah, I'll take a helmet.