The rule doesn't prohibit hitting a defenseless receiver. The rule prohibits hitting a defenseless receiver "in the head or neck area."
This is widely misinterpreted by media and fans alike. This hit made no contact to the head or neck area, therefore it should not have penalty. Unfortunately, officials have become overly sensitive to this particular rule and throw the flag every time they see a big hit on a receiver that is above the abdominal area.
These calls need to be reviewable and I believe that, as a result of many bad calls this season, we may be headed in that direction.