The initial conceit (and a problematic one, at that) with nearly every war film is that, almost without fail, the protagonist of the film will be the Hero. The Hero ranges from the obvious (John Wayne in The Green Berets) to the obscure (Kirk Douglas in Paths of Glory.) The Thin Red Line disregards the concept of the Hero, placing its focus instead on the act of war itself. Sergeant Edward Welsh (Sean Penn) states early on that one man alone cannot make a difference - in war, and even in life. He proceeds to, heroically and amidst substantial gunfire, attend to the aid of a comrade dying in the battlefield. But Malick is quick to point out that Welsh is not a hero - when this supposed hero is confronted with the possibility of decoration, he adamantly opposes the idea. His refusal contends that his acts were not heroic. Rather, they maintain that this is duty, this is expected, this is human decency. And therein lies the problem with the Hero. Heroism implies that mediocrity by choice is acceptable, that there exists such a thing as "just good enough", that allowing a comrade to die without aid on the battlefield is ok. Malick's film implies that such a concept exists only in the hearts of the selfish.
The Thin Red Line opens with the focus of the film on Private Witt (Jim Caviezel); Witt narrating while images of a jungle bucolic amble on. The Private speaks of good and evil, and innocence lost. He says, "How'd we lose that goodness that was given to us?" This is the thesis of the film. The hero is absent in The Thin Red Line because the hero is absent in war, and in life; all that exists is the possibility of momentarily attaining that goodness. Witt resides in the aforementioned jungle bucolic, having gone AWOL. The peace he sees there he equates to a whole different world. This is his heaven, a place where the goodness given still exists.