I think the authors message about society is weather does not matter what or how they look its about there personalty a saying would be dont judge a book by its cover. For example in the movie, Fionas mom and dad were waiting for her supporting beautiful daughters but when they arrive they see two ugly ogres the dad was very disappoint and in this case judge them by what they look like. It wasnt just the dad who treated Shrek bad he sent a pussy cat to capture Shrek so that prince charming, the godmother presented to help shrek but she just wanted him far away for charming to marry Fiona.
Now as you can see all people except few did not try to hurt shrek because they knew him and liked him for his personalty. Now in the first movie they were scared but they got to know him and ended up liking him so it does not matter how ugly, scary or tall you are it could end up to be the nicest person you will ever met