Interesting editorial in the NY Times today by former Broncos receiver Nate Jackson, explaining why Harrison is understandably confused and upset about the fine and the proposed rule changes.

The whole thing is worth a read, but this especially jumped out at me:

Some say players should block and tackle with the shoulder pads instead. Doing that means choosing a side, trying to hit an opponent with the left or right shoulder. That technique will get you cut by any professional team before you can begin to perfect it. It uses only half of your body and half of your strength, and it removes your arms from the equation. In a head-first hit, the arms are free to follow the first contact with a bear hug that brings the opponent to the ground.

In other words, players lead with their heads, so there's a lot of helmet-to-helmet stuff going on all the time, and it's difficult to avoid without changing the entire way defense is played - which is essentially what Harrison was arguing.