I mean am I the only one who knows of many horses that aren't really fond of that part of tacking up? Once you get through that they are fine and go about their business. Yes it needs to be addressed you don't want to get bit and let the horse get away with it. (unless of course its a pain issue)
Just my two cents for today.
I got a horse that already had this bad habit long before I got her. She tried several times to bite me when I tightened girth. (and I checked for pain, saddle fit, etc) and determined it was just her protesting going for a ride. After using my voice, etc. I just smacked her the neck very quickly and sharply and guess what she never did it to me again.