I am of two minds. On the one hand, it is clearly taunting. They are not doing it to celebrate a great play. They are doing it to rub their opponent's nose in the dirt. I am not sure why anyone would want their child to behave like that. And, if we would expect our children to behave better, then it is not unreasonable to expect the same of grown men.
On the other hand, most of these guys are talking trash all game long. The least of their offenses through the game is probably a hand gesture like this. You see it everywhere. A RB runs over a guy and he gets in his face. A WR makes a catch and immediately gets in the face of the DB that he beat. Same applies on the other side of the ball. Talking trash isn't new, and it is generally accepted, but it is most assuredly taunting.
IMO, the taunting rule is put in place to avoid the kind of bench clearing nonsense that we see virtually every year in the Egg Bowl. It amounts to babysitting men because they cannot be trusted to act like men. But what happens if we stop enforcing the rule?