Helmet contact per se is not illegal. As a matter of fact, you will see helmet-to-helmet contact on just about every running play in the league, because ball carriers dip their heads in anticipation of a hit. They do this both to punish the defenders and to protect their necks.
Because of that behavior, the NFL has never said helmet contact with ball carriers is illegal.
Once a receiver takes two steps he is a ball carrier, and is no longer protected as a "defenseless player."
Your claim about Burfict is nonsense as well. Burfict was three steps away from Brown when the ball went over his head. In the NFL players launching at QB's and receivers are permitted ONE AND A HALF STEPS, anything further away than that it's expected that the defender has time to pull up. Doesn't matter when Brown came down, all that matters is how far away Burfict was when it became clear that the ball was uncatchable. He had plenty of time. He's a POS who goes out of his way to injure other players.
Cut the arrogant BS or learn how to read, Mr. Z. I was not talking about Burfict, but about Brown. Thanks.