This is a physical game. You are trying to hit people hard, cleanly and within the rules. That is very much the name of the game and when it is not it becomes touch football.
Trying to deliver the hardest legal hit you can is perfectly legitimate. If you don't like that concept, don't play the game. On the other hand, intentionally going low to take out a knee, alterning your agnle of impact to deliberately go after the head, piling on after all the whistle are all clearly things that cross the line from playing hard within the rules to trying to deliberately injure a vulnerable player.
That safety from the Ravens might be half right. In 30 years there may be an NFL but it may be unrecognizable compared to what it was up until recently. Maybe it will look like the Pro Bowl.