Denethor is an interesting character. He’s one of the only (if not the only?) antagonists who is not evil. Denethor’s flaw is that he has given up hope.
Denethor is the only cynic in middle earth.
Denethor is the only cynic in middle earth.
And the defenders at Minas Tirith, Saruman, even the elves - the whole lot of them in middle earth have given up hope.
Despair is one of the key themes running through all of Tolkiens work. Denethor was far from alone