Well since we're offering opinions here I'll throw my hat in the ring. The moral of the film is summed up in what Shane tells Jean Arthur when he's teaching Joey how to shoot -
"A gun is a tool. No better or no worse than any other tool. An axe, a shovel or anything. A gun is as good or as bad as the man using it - remember that."
The scene of him riding through the cemetery at the end shows that he was justified in what he did. An inoccent man was in that cemetery because of Rufus Ryker and his hired killer Jack Wilson. They were planning on murdering Joe Starrett as a way of getting the other homesteaders to give up and move out.
Shane was a good man who did what needed to be done. There was no law in the territory to protect these people. However he had to move on at the end, because he knew by staying other gunfighters would come around looking for him to prove they were faster than he was.
As Shane is riding away we know from what Joey says to him he was only hit once and that was by Rufus Ryker. "He'd a never hit you if you had seen him. He'd a never even cleared his holster..." Morgan Ryker tried to hit him with a rifle.
Shane lived and perhaps went on to use his gunfighting skills for something good rather than robbing and murdering.
Edited by Walsh61, August 25 2013 - 04:22 PM.