I can see @NickJ's point, with the H&S rules nowadays it would be virtually impossible to overfill a terrace to the point where nobody can see, so any issues were probably caused by people massing in the wrong places and leaving other areas relatively free.
On the other hand, you cannot really blame anyone for not 'just pushing their way through' - it's not 30+ years ago any more, people don't really understand how a packed terrace works any more and it was the old 'terrace protocol' and such attitudes that indirectly caused a lot of problems in the past. It was an amazingly exciting experience, being crammed onto an overfilled terrace, not being able to touch the ground some of the time and essesntially being at the mercy of the crowd as to where your movements took you, but it's not something that could have been allowed to continue.