Totally agree... Here in Phoenix, AZ(AKA Haiti during the summer) it gets to be about 115 degrees... with out a face cover, it feels like it is cooking the insides of you nostrils!!! I prefer a full face helmet...
Plus, on the other front, I used to ride to lunch without my gear on, then one day I caught a little gravel spot and the back end slide about half a foot over it... no big deal... just scared me a little... At 25 mph around a corner, to take a spill with nothing on... ouch! I always wear everything I have... I do step down to an AGV mesh jacket in the summer, but I am saving for a better one...