The morals were different for everyone. For me, mother 3 did have good writing, but still paled in comparison to earthbound. Mother 3 had a lot of different themes people can take from it, I think one of the biggest ones was moving on and dwelling in the past. Porky was a villain because he never moved on from Ness, or had his own coming of age story. Lucas grew as a character because he quit feeling bad for himself and realised what he had to do.
That being said, mother 3 just couldn't replicate what earthbound had. Earthbound was a true coming-of-age story, and it used more abstract ideas and themes to illustrate this, such as the pop culture references and imagery. Mother 3 attempted to recreate these themes, but instead of using Earthbound's idea of "a story told through the mind of a child, some areas such as loss of innocence will be dark" they went for very literal dark scenes.