The Fall of Denethor

[Mister Underhill]

Clausewitz, eh? Take this Clausewitz:

A great part of the information obtained in War is contradictory, a still greater part is false, and by far the greatest part is of a doubtful character. What is required of an officer is a certain power of discrimination, which only knowledge of men and things and good judgment can give.

Perhaps you're right that it was not necessarily the use of the Palantír that is condemnable -- perhaps this extreme method of intelligence-gathering was called for -- but again we must come back to Denethor's pride and resultant poor judgment.

Rather than share the intelligence he gained with learned counselors and allies for analysis, Denethor hoarded his knowledge, preferring instead to feed his pride by being able to project an impression of quasi-omniscience. A free exchange of information with others who could be more objective than himself may have prevented Denethor's fall into madness and disgrace.

Denethor instead deluded himself into thinking that he was at least the personal equal of Sauron and could not be deceived by him.