That's complete nonsense. Gronkowski was basically defenseless at the time the hit was made, having just turned back for the ball. Ward was no more at risk for injury himself than any other play. From his own mouth he went low to avoid a fine.
DBs have been tackling big backs and receivers for decades. This going low repeatedly is new. Until recently, a player who did that was labled dirty, and rightly so.
An article I read this morning said severe knee injuries are up 60% from just 2 years ago. That speaks for itself. NFL has to do something if they expect to keep a viable product on the field.