TAYLOR: I just wanna be anonymous like everybody else, do my share for my country, live up to what grandpa did in the first war, dad did in the second.
Taylor is initially influenced by traditional ideas about warfare being a chance to serve one's country and do what's right. But Vietnam was a whole different ballgame, and the relative invisibility of the enemy in this film suggests that there really wasn't any "evil" to fight. Taylor's words come to seem hollow as we come to see that there's no point to his sacrifice.
BARNES: Elias is a water walker, like them politicians in Washington trying to fight this war with one hand tied around their balls. Ain't no need or time for a courtroom out here
War is a lawless, evil zone, a place about as far removed from the civilized world of the "courtroom" as a place can be. Winning a war takes decisive action, and politicians seem unwilling to permit it. They would rather try to fight "with one hand tied around their balls."
TAYLOR: She's a f***ing human being man, f*** you… f***ing animal… all of you are f***ing animals.
This is what Taylor says to his fellow soldiers when he discovers them raping a Vietnamese girl. In this movie, war makes "animals" out of human beings. It destroys all that makes them human and reduces them to their most primal of instincts.
CAPTAIN HARRIS: I can promise you something, if I find out there was an illegal killing, there will be a court martial
Harris reference to a court martial rings hollow in the lawless world of Vietnam. We know that in this war-torn landscape, the threat of discipline is at best empty. The reference to an "illegal killing," however, foreshadows Barnes killing of Elias, and Taylor's killing of Barnes, both of which are, technically speaking, illegal.
ELIAS: What happened today is just the beginning. We're gonna lose this war…We've been kicking other people's asses for so long I figure it's time we got ours kicked
In war, there's always a winner and a loser. Elias is the voice of reason throughout the film, the voice of prophecy, and his assertion that "we're gonna lose this war" is the film's way of ensuring that the whole thing was losing effort, for Americans and Vietnamese alike.
TAYLOR: The morale of the men is low… A civil war in the platoon, half the men with Elias, half with Barnes… I can't believe we're fighting each other
Taylor hits on one of the film's biggest themes: the very real "civil war" within the platoon itself. The second of the film is given over to exploring this destructive, internecine conflict. In some ways, this is the real war in Vietnam.
BARNES: Now I got no fight with any man does what he's told. But when he don't, the machine breaks down. And when the machine breaks down, we break down. And I ain't gonna allow that, from any of you
Barnes describes the military chain of command very eloquently here. The platoon is like a "machine," and if guys don't follow orders and decide to do what they want, well the machine breaks and everybody dies. Successful warfare depends on the machine being well oiled, so to speak, which means doing whatever Barnes says.
KING: Somewhere out there is the beast and he hungry tonight.
What is the beast? The enemy? The jungle itself? The divisive spirit in the platoon that threatens to tear it apart? The answer is… all of the above. The beast refers to the entire spectrum of destructive things the men of the platoon face throughout the film.
TAYLOR: We didn't fight the enemy. We fought ourselves, and the enemy was in us. The war is over for me now, but it will always be there, the rest of my days.
There's a reason we don't see too many enemy troops in Platoon, and Taylor makes that reason clear at the end: the real enemies are the soldiers themselves ("ourselves"), the guys in the platoon who do more to hurt their fellow brothers than any NVA troop could ever do. The "enemy… in us" is the civil war Taylor talks about earlier in the film.