The replay looked to me like Hardy led with his helmet into the QB instead of his pads. You can see his facemask go right into Palmer's ribs. I don't necessarily disagree with that call, but the no-call on Cam was absolute bullsh*t
What you said above is key: HE PUT HIS *FACEMASK* INTO PALMERS RIBS.
NOT the crown of his helmet.
Leading with the crown of your helmet (i.e. spearing) is and should be a penalty.
Keeping your head up and putting your facemask into the torso of the player you're tackling? Hell, that's just textbook football.
It WAS a violent hit. Hardy was bringing the pain and intentionally so. But it sure as hell wasn't a cheap shot and it should NOT have been penalized.