Mr Winter does not go easy on the Steward of Gondor. The post levels accusations like “deluded”, “lack of self-knowledge”, and “given to fantasy”. There are two specific charges against Denethor: use of the palantir, and planning to use the Ring. The post says it’s because Denethor’s Numenorean arrogance (stipulated by the defense) convinces him he’s stronger than either, and so he can turn them to his own ends. This kind of misjudgment, the argument goes, makes him the bad guy.
As I mentioned over there, there’s nothing in the text that makes us conclude Denethor thought that he was greater than the Ring or the palantir. The evidence says, rather, that he made a considered judgment that using the palantir is better than not using it. I agree that “the Ring holds no terror” for him. If not using it would be the greater evil in Denethor’s judgment, he would use it. What does Tolkien say in his favor?
Denethor II was a proud man, tall, valiant, and more kingly than any man that had appeared in Gondor for many lives of men; and he was wise also, and far-sighted, and learned in lore. Indeed he was as like to Thorongil as to one of nearest kin … When Denethor became Steward (2984) he proved a masterful lord, holding the rule of all things in his own hand. He said little. He listened to counsel, and then followed his own mind.
LotR, Appendix A(iv)
Coming from JRRT, this is high praise. Hell, I’d even vote for him myself. On the negative side, we have Gandalf’s post-mortem:
Though the Stewards deemed that it was a secret kept only by themselves, long ago I guessed that here in the White Tower, one at least of the Seven Seeing Stones was preserved. In the days of his wisdom Denethor would not presume to use it to challenge Sauron, knowing the limits of his own strength. But his wisdom failed; and I fear that as the peril of his realm grew he looked in the Stone and was deceived: far too often, I guess, since Boromir departed. He was too great to be subdued to the will of the Dark Power, he saw nonetheless only those things which that Power permitted him to see. The knowledge which he obtained was, doubtless, often of service to him; yet the vision of the great might of Mordor that was shown to him fed the despair of his heart until it overthrew his mind.
No way is Gandalf a disinterested observer.  This is a funeral speech for political purposes, like Marc Antony’s over Julius Caesar, but if we’re careful we can use it. Disregard subjective judgments about wisdom and foolishness, and note the contradiction: there’s only one sentence separating “…Denethor would not presume to challenge Sauron…” from “He was too great to be subdued to the will of the Dark Power…”. Let’s note that not using the palantir to challenge Sauron means Denethor was using it for general reconnaissance, which was “often of service to him.” He knew how to use tools, even ancient artifacts.
Mind to mind, the Steward of Gondor was a match for Sauron, where Saruman was not. This is a clue to Denethor’s place on the good-guy/bad-guy scale. Saruman was caught (LotR, III.xi) because he wanted power beyond his due. On the contrary, just like swindlers can’t con an honest man, Sauron can’t subdue Denethor. Denethor has earned his power, by birth and by decades of just rule. He’s not looking for more than he has.
Middle Earth and the Cold War
As it happens, I met a real-life Denethor. James R. Schlesinger was President Nixon’s Secretary of Defense, President Carter’s Secretary of Energy. (For my readers outside Washington, DC, that means he was in charge of the nuclear weapons.) In that meeting I was only 5% more senior than Pippin, and believe me: “between two such terrible old men” is an understatement. I wore a tie that matched the wallpaper and I kept my mouth so firmly shut it’s a wonder I could open it again afterwards.
The One Ring is not an allegory for nuclear weaponry, but it’s perfectly valid to use the Ring to think about what nuclear weapons mean. Working the other way is valid, too. We now know lots of stories about how people behaved when they were given world-destroying power, and we can use that to think about what the Ring might do.
When Sec. Schlesinger took office, the official strategy of the US was “Mutual Assured Destruction“. That is, the USA knew that the USSR wouldn’t attack us because we’d obliterate their cities. And the USSR knew we wouldn’t attack them because ditto. Yes, technically both of us were threatening war crimes. Schlesinger saw that there was a fundamental moral problem with that, which leads to a military problem: will the troops carry out that order? What kind of monster would give it? (cf. “The Last Command” by Arthur C. Clarke) Schlesinger started the process of turning US strategy towards counter-force operations, which improved the deterrence by concentrating the threat on the people who would actually be involved in starting the war. It worked. I was of draft age during the last, most-stressful part of the Cold War. I won’t even pretend to be objective in my approval.
Because of this history, which JRRT didn’t have, I believe Denethor when he promises, “It should have been kept, hidden, hidden dark and deep. Not used, I say, unless at the uttermost end of need, but set beyond his grasp, save by a victory so final that what befell would not trouble us, being dead.” All eight US Presidents and five Soviet Premiers did that in their challenge. All the Secretaries and Ministers of Defense, as well. Zero leaders on either side failed to.
Faramir passed the test of the Ring. Might not Denethor have passed it, too? He was greater than Faramir when he was young, and only grew in wisdom and power after that.
And pride, alas. Sauron found the tragic flaw. He couldn’t beat Denethor face to face. He couldn’t thwart Denethor’s intelligence operations, but he could mislead them. Lying through the palantir’s video feed may have been Sauron’s greatest accomplishment. I don’t doubt that Denethor experienced a direct frontal assault on his mind from Sauron, withstood it, and thought that he had won. That’s when one is most vulnerable to deceit, and where Sauron is strongest. Winter says this means Denethor “disastrously misjudged his own capacity”; I say this is the kind of conflict we see in the real world, between two evenly-matched adversaries. Where you can’t win by strength, you try trickery. Nobody misjudged anything.
Back in the real world (as I commented on Winter’s blog) I look at leaders, and I see one thing they all have in common. As a rule, the good ones are all conscious of their responsibility to the innocents they protect. Denethor is one of our leaders. He looks at the worst that can happen, and chooses the strategy that turns out the best if everything goes wrong. (Operations researchers call this “minimax”.) If cost-benefit analyses existed in Gondor, he’d insist on having them on his desk. I feel like I understand Denethor, because I’ve met people like him. By my lights and theirs, he’s doing the right thing. Gandalf breaks that rule. He sends the Ring into Mordor, knowing that the chance of devastating failure is at least as great as the chance of success. What kind of person does that? The hero of a romance, that’s who. Gandalf’s plan would never be chosen by someone who doesn’t have supernatural support, which is Tolkien’s point.
Also on the comment thread, “The Hapsburg Restorationist” (username checks out) cites Letter #183, that “Denethor was tainted with mere politics”, and Winter replies with the observation that “Denethor is a politician and Aragorn is a king. We all need to learn the difference between the two in our time.” I hope this post demonstrates that we’ve done so.
 “Denethor” is an anagram of “dethrone”, which I never noticed before but others did.
 Gandalf learned compassion and pity from Nienna, but the books are silent about where he learned intellectual snobbery. I’m guessing faculty meetings.