What western movie is this?

I cant remember what its called but I remember that there is this man that is terrorizing this family in this small western town. I'm pretty sure he wore dark ozzy osbourne style sungles. The scenes I remember are at the beginning the boy from the family is on the town prostitute or something showering outside. In a different scene the main villain is sitting outside of the family's with either a guitar or a banjo singing the battle hymn of the republic (glory, glory hallelujah). In another scene there is this man that I think is either retarded or portrayed as an idiot and he is digging a hole I think and the villain comes up behind him and the retard/idiot shoots him, which is meant to be a surprise to the viewer since hes so stupid.