I agree punching should not be within the rules, and by the way it never actually was.
For mine there was no need for a no punching rule as it was already illegal under the rules of the game. Just ask Gifty how he went in the semi finals in 2011. He didn't play because he got sent off and suspended for punching. That was on his way to the sideline after he was sin binned on suspicion of punching.
Similarly, slapping has no place in the game.
Players are out there to play football. High tackles, lifting tackles, even shoulder charges CAN be more dangerous but they will always be a part of a collision sport as they can happen inadvertantly while trying to play the game within the rules.
Punching, slapping, head-butting, gouging, chicken wings, leg twists, "actual" crusher tackles, even pushing and shoving are all just various levels of violent behaviour that have nothing to do with the sport and the referees should be able to use the sin bin, penalties or even send offs to deal with any of those acts on their merits. They shouldn't be bound by some black and white rule that says they have to sin bin for a punch but can't do anything about a slap because people will complain the game has gone soft.
I don't hate Ennis as much as most fans seem to. I reserve that emotion for others who have done worse than niggle other footballers during a game. Having said that though, if I was the ref last night he would have been off for 10. You don't slap someone by accident and trying to bait someone is not a good enough reason for assault just because you are playing sport.