The left side of the brain controls the right side of the body. It also controls language. There’s a theory that that’s why the words for the left hand (and left in general) are usually associated with evil (“sinister” in Latin means “left”, for example), while words for the right are associated with good (“dextrous” comes from the Latin “dexter”, meaning “right side”). The left side of the brain might be literally disparaging the side of the body it doesn’t control, while praising the one it does.