There are two modes of warfare in The Return of the King. First we've got the widespread civilian destruction that Sauron wants to cause by tossing bombs over the city walls into Minas Tirith. Then, there is the more gentlemanly direct combat between men with swords that the Good Guys (and especially the Riders of Rohan) seem to prefer. Yet, even if hand-to-hand fighting is more honorable than throwing darts at combatants from above (we're looking at you, Lord of the Nazgûl), it's still not a good thing. Despite the fact that the warrior rage the men of Rohan show is on the Good Side, there's still something awful about loving fighting in Tolkien's book. Perhaps it's because no matter what, war is total. Its effects can be felt right down to the hobbits left behind in the Shire.
By emphasizing the emotional bonds among the people fighting on the good side, Tolkien implies that the only way to make something as awful as war even slightly bearable is through strong friendship.
Mordor's use of explosive siege weapons and dart-throwing Nazgûl represents a critique on Tolkien's part of the massive destruction caused by the bombs and airplanes of modern warfare.