It's to protect the defensive players as well. Proper tackling should be taught at every level instead of killshots with spearing your helmet at a defender; look no further than Ryan Shazier of the Steelers (paralyzed from using his helmet to spear a running back; hell, Countess got himself concussed on that aforementioned play along with Goodwin). Using the crown of your helmet (as Joseph did with both Higbee and Hockenson's knee) as the primary weapon doesn't just hurt the players you hit; it can hurt you. I know this shit, and I never even played.
Call me soft all you like, and yes, I saw Haynesworth, Burfict, Suh, etc. all play and do plays outside of the scope of the game. Yes, that's dirty, but there's different levels of dirtiness. Just because Haynesworth stomped on Gurode's helmet doesn't mean that Joseph or Branch should suddenly be absolved for using their helmets as weapons. No, he didn't receive a fine, but that shouldn't mean that what he did wasn't dirty.
Yeah, I'd be just as pissed as Stafford was in that situation.