Just to chime in here, when I was completing the theory half of my referee's certificate, Casey Badger running the course, she told the story of a young high school kid who'd suffered concussion from a shoulder charge and other contact with the head.
This kid, turned out for his school in a match on Friday, suffered concussion from a shoulder charge. It knocked him out, told not to play again for a while and see a doctor as soon as he could. Next day, doesn't tell his parents or anyone outside his school, plays for his club in Union that Saturday. Gets hit in the head, knocked out again, same thing happens (told to see a Dr. not play, etc). Come Sunday he hasn't told his parents again or anyone else, turns out for his League club, gets hit with contact to the head again, this time he... well is no longer alive as a result.
Was all in the papers and basically, despite the League club being the last one he played for, eventually reported that because he had played these 3 games in a row, suffered repeated knocks to the head, concussion as a result of each one obviously, and most of all not told anybody at any of these 3 separate clubs, that was the cause of his fatality.
Point being, you can get smashed in the head, by a shoulder charge (which is why they banned it isn't it, it can & will cause severe trauma to the head eventually and result in concussion, more often if legalised than banned), you will pick up a concussion as a result, and even if you can get up and walk around 4 minutes later, the severe dangers that come with concussion as a result of a shoulder charge or other head contact, can show up long after the event. Even without playing 3 games in a row, the massive repercussions of suffering a concussion are really, quite seriously, severe and always potentially life threatening. Doing your first aid certificate, they'll teach you head trauma is always one of, if not the most, threatening of all injuries you'll potentially have to treat, because of it's effects.
So yeah, the less contact with the head the better, and by banning the shoulder charge at all levels, you have a greater chance of avoiding that happening than you would by keeping it a legal tactic.