There are aspects of the game which need to be policed and fighting is one of them. They are not banning it, because you can't; punching is a response to an action. It is likely that a foul has been committed and a person will respond to that foul.
If it is a punch, then that player must understand that he will be sent to the bin for doing so; end of story. I am not saying that banning the biff will stop the biff; it just means there is a consequence.
I was never a person who could ever consider himself a fighter and many a punching bag can testify to that, so my perspective is a passive one. In an aggressive sport where heavy contact is constant, tempers are going to flare, but it doesn't mean you have to punch someone in retaliation.
Rugby league has enough fair contact in it to balance whatever you may feel is an indiscretion on you. Tackling someone fairly on their blind side is always a leveller and an action guaranteed to get spectators off their seats. I read a comment that New South Wales lock Greg Bird made this week where he states that if he was punched, he would punch back.
This simplistic response is instinct and it takes time to over come such a response. If Bird was eye-gouged,would he gouge back? He wouldn't, as the game doesn't allow this to exist anymore. Bird's response would be to protest to the ref and ask for action; the game has moved on from that type of play.
The same will happen in time with punching and it is not sterilising the sport, as punching does not define Origin football or rugby league in general.
Implementing the rule does not mean it will not happen but how long will punching continue if your team loses the game because you're in the bin? How long will you be selected if you choose to punch? Give it time.