It may be true that the story of the Ring is less morally ambiguous than the average realistic novel, but that’s primarily because Tolkien wasn’t especially interested in the problem of knowing right from wrong. His concern was to explore the psychology of the moment when you know right from wrong but aren’t sure whether you have the courage and fortitude to do the right thing.
Modern liberalism likes to think that all our problems are epistemological: we are afflicted by never knowing with sufficient clarity what we ought to do. Our fictions tend to reflect that assumption. Tolkien, not being a modern liberal, thought it more interesting to explore situations when people know what they need to know but may lack the strength of will to act on that knowledge.