I somewhat agree with bsms on "wussiefication"... (LOL! Love that vocab)
I mean, I'd have no problem riding my trainers bombproof pleasure horses helmetless, because the chance of them spooking or spazzing out is extremelyyy looowwww... However, riding my more spunky pony; I'd rather wear the helmet than take the chance. He's had this habit of rearing when we enter the ring (ring sour) and he's a bit buddy sour yet too, and although it's getting way better, I'd rather not risk it.