Natural instinct if you mean RBs start turning themselves into missiles routinely at a young age that it becomes second nature upon impact then I agree.
Right...it's a terrible habit, and unfortunately because of the stupid way the rules are interpreted basically allow offensive players to lead with their head while defensive players better HOPE their head doesn't accidentally make contact with his helmet during the collision.
Take this run by Trent Richardson. It's an extremely powerful hit, but he basically spears the defender who actually goes in without leading with his head. No flag despite the fact Richardson de-helmeted the guy when the crown of his lid rammed the defender in the jaw. Had the hit gone in reverse and the defender had hit Richardson in the jaw with the crown of his helmet, the guy would have been flagged and then fined. LINK
As for Ridley, he didn't so much lead with his head as ducked it down and he got popped...but much the same way defenders are having to learn not to go in with their face at the ground, so must offensive guys. A good first step would be flagging BOTH sides for doing this if they're honest about it being a safety issue. Thankfully Ridley will be ok...I was really worried there for a minute...