People seem to be missing some key points.
Tackling so you make contact with the head has never been legal. However it was not really enforced and so people became used to big hits, which have developed majorly over the last 10-15 years, where the player is forced back and momentum is stopped. Majority were around the chest, but quite a few hit the head. However unless it was serious it was seen as part of the tackle. However (and this is the key point) it also led to an increase in concussions and serious head injuries with extensive research highlighting that the majority of concussion occurred as a result of the tackle. Therefore WR had to act to protect the players and so they wouldn't be left open to law suits. (You choose which they cared more about). So they implemented their new rules and hoped things would change. It didn't and over the last 2 years players have continued to hit hard and around the chest, which can lead to high tackles and more concussions. Therefore because it wasn't changing WR had to get tough and didn't want to be seen to be soft on head injuries. So they made the new framework and asked the refs to rigidly enforce it during the world cup. The intention was that if players are aiming for the chest and end up hitting the player they will get a card of some kind and therefore players will realise they can't take the risk and will tackle lower. However players have been coached this way since they were young and so it's hard to change habits easily hence the number of cards. On top fans are so used to these big hits going unpunished (pundits too) that they seem to think they are acceptable.
There is no controversy about high tackles and the enforcement of the law ruining the game. It is not about stopping players tackling hard, but getting players to tackle lower and correctly to avoid the increasing number of head injuries. The controversy is that WR stupidly decided to get strict during the world cup and so detract from the main event. Instead of people discussing the games, they ended up discussing the high tackles.