I'll say upfront that I am a big proponent of player safety. I don't think the game of football will survive unless increased safety measures are taken. Player safety rules don't ruin the game; they preserve it. And if you are like me—someone who thinks that player safety is quite important —then you should be a fan of the new rule. I can see two potential problems with the new rule, and I'd like to defend it from both.
Problem No. 1: The actual rule itself
I can see why people are nervous about taking moves away from a running back—or any offensive player for that matter. The line of argument against the rule states that this hurts a RB's ability to protect himself. But I'm not buying it. The rule clearly states that only contact from the very top of the helmet is illegal. Contact in that manner goes against all the training I learned playing football. It's bad technique. Hitting with the crown of the helmet can leave a man paralyzed or worse.
This rule does not affect in any manner the contact that occurs from the facemask, side of the helmet, or the forehead area. A running back can still sink his hips, bend his knees, and run straight into the defender. He just has to have his face up, and not down. The vast majority of RBs already play this way—that's why they are pros.
I just watched about an hour of Frank Gore footage on YouTube, and it basically confirms what I'm saying. Outside the tackle box, first off, he usually tries to cut. But when he does make contact, it's frequently with either the shoulder, facemask, or the forehead portion of his helmet. He only really uses the crown of his helmet on the goal-line, which is within the tackles. The rule simply forces players, who already use good form most of the time, to use good form at all times.
Problem No. 2: Application of the rule by referees
This is the most problematic issue in my mind. I will admit, refs might not be great at seeing this in game time, at first. But as with any newly introduced rule, that's only part of the learning curve. By and large, the refs have gotten remarkably good at the new contact rules. Do they mess up sometimes? Absolutely. I wouldn't mind having these types of penalties be reviewable to reduce this margin of error. But in actuality, the refs will learn to get this right, just like they learned how to call hits against a defenseless receiver right. The amount of safety this can bring to players both in the short term and in the long term makes up for a missed call here and there.