The changes they are making to the rules in the NRL and SL are simply bringing consistency by making contact with the head illegal, and - as it always should have been - the responsibility of the tackler to avoid. The reason for the change is down to possible future legal action. Its all very well players being gung ho about shoulder charges when they're young and fit, but given the medical evidence about the long-term consequences of hits to the head, the sport would be laying itself open to all kinds of law suits down the track if despite that evidence it didn't penalise players hitting the head.
The shoulder charge itself isn't being penalised - contact with the head is.
I've never understood the complete inconsistency that its apparently 'bad' to swing your arm into someone's face, but OK to hit someone square in the face with your shoulder, including all your body weight behind it. Suggestions that the game is going soft if that sort of contact is banned are ridiculous - how many shoulder charges are there during the average game? How many actually come off? They may look spectacular, but given the potential for injury (including to the tackler for those that do it regularly) and the high chance of being penalised or simply missing completely, I suspect coaches frown on them now.
Nobody is saying you can't go for a big hit, just that if you hit someone in the head then it is likely to be a penalty at least. If the tackler can't avoid smashing someone in the head then that's bad technique, just as a swinging arm is.