My theory is that he had already had murderous tendencies for most of his life, so he jumped at the chance to channel his aggression into legally killing for the Marines. He only realized what a mistake this was when he actually got to camp, and found out how terrible he was at everything military-related that didn't actually involve killing. His skill on the firing range seems to indicate that he had prior experience with guns, so it's definitely possible that he'd tried to prepare for a future shooting spree when he was younger. His murderous breakdown at the end wasn't the result of stress and anger at all—it was just him finally letting go of the aggression that he'd been holding back for years, since he realized that he had nothing left to lose.
- Did he enlist or was he conscripted? And besides, when put under pressure, people break in different ways.
- The Marines, Navy and Air Force have never had a draft. And even then, less than 1000 Marines were drafted in Vietnam or World War II, something which amounted to a recruiter "volunteering" Army draftees to meet quotas in both wars. So he enlisted, he wasn't drafted.
- Many men joined the Marines because they knew they were subject to the draft, and tried to circumvent going to a bad Army unit. The belief was if they are going to fight in Vietnam anyway, may as well be in an all-volunteer outfit. So in essence, many Marines were unwilling, or at least less than enthusiastic volunteers.
- Where do you people get all this? The Marines did a draft just like all the other branches did, in WWII, Korea, and Vietnam. It's standard policy that if one branch does a draft, they all have to. The numbers were usually smaller, but the draft was present. And then Project 100,000 came along, which is probably how Leonard got sucked in.
- About 5% of Marines (vs. about 25% of Army soldiers) were draftees, so there is a roughly 5% chance Leonard was a draftee. Low, but not impossible. It's also entirely possible that he was impacted by Project 100,000, but that has nothing to do with whether he was a draftee or a volunteer: the lowering of AFQT standards applied to both.
- The book the movie is based on is careful to describe Pyle as a very innocent soul. He also isn't out of shape, and is actually described as being skinny. He's just 'slow' and needs to be reminded to do everything. His breakdown is also clearly depicted as a psychotic break: he believed his rifle was talking to him and he shoots the drill sergeant because he looked at 'her' in a way he didn't like. This theory can still make sense within context of the movie though.
- Literally millions of Americans grow up shooting rifles who have no desire to murder anyone. Him already knowing how to shoot (or not knowing and just being naturally talented) isn’t indicative of anything. For many people, target shooting is a nonviolent (shooting people is violent, shooting a paper circle isn’t) recreational activity. And as I already said, he may have never touched a weapon before and just had a natural talent for marksmanship. That happens sometimes.
- Sure, but then he develops Vrolik syndrome, becomes immortal, develops a talent for piloting spaceships, and mellows out a lot.
Joker seems to really, really want to fit in with Cowboy’s platoon, despite being a “POG” reporter who only occasionally sees danger. They seem okay with him at first, and he doesn’t cause any problems as long as nothing happens that likely means he might get killed, but the moment things really go sideways, when they take a wrong turn in Hue City, Joker immediately turns into a chattering wreck. His best friend Cowboy has to give him a not-at-all-friendly “Joker, shut the fuck up!” before his nervous talk starts affecting morale or discipline. Even when hunting the sniper, Joker seems less motivated by any desire to fight the enemy or avenge his friend than by the fact that Animal Mother will probably shoot him if he doesn’t. To use Animal Mother’s own words, Joker talks the talk, but he doesn’t walk the walk at all.
Amongst the gamut of fake veterans are cases of men (and women) who did in fact serve in the military, but claim to have been Special Forces running classified operations when they were actually supply clerks in the safe rear area, or claim to have been career soldiers when they actually were kicked out for disciplinary problems after only a year, or they just claim rank and medals they never earned, and these “embellishers” often tell the most colorful, war-crime-laden stories about their supposed experiences, with some even publishing bestselling books. Joker clearly wants those around him to think he’s something he’s not. He will probably carry that with him when he returns to civilian life, spinning Rambo-esque tales of his alleged combat prowess as much to pro-war kids who want to believe in action movies as to anti-war protestors who want to hear about atrocities—as long as they give him the attention he wants, he’ll give them what they want.
This is, however, contradicted in the book The Short-Timers, on which the film is based. He is eventually promoted to Sergeant, and takes over the leadership of the Lusthog Squad. Animal Mother becomes the point - because he likes doing it.
- In the book sequel The Phantom Blooper however, Joker had issues adjusting to civilian life, and went back to live in the VC village he spent time with as a POW.
Thus when Leonard Lawrence showed up and proved himself an expert with the rifle as well as managing to sneak jelly doughnuts out of the mess hall into his foot locker, Durrane and Seaton found their ticket to ending Hartman's abuse. Forcing Hartman to be more hands on and take the reins off them, Durrane and Seaton became willfully lax in their security checks once leaving the rifle range to allow Leonard to smuggle the live rounds back to his foot locker. And they willfully disregarded standard safety and security procedures to leave a key for Leonard to unlock his rifle from his bunk on the last night of 3092's stay on Parris Island before the buses would take them out for advanced training the next morning. They did know that Leonard was taking enough rounds for a full magazine, but disregarded it so that it would result in Leonard killing only Hartman and himself with Davis (Private Joker) powerless due to his compassion for Leonard.
If they were going to end up drummed out of the Corps and court-martialed over what they did or did not do, they would at least ensure Hartman was brought down with them in the bargain. This was a farfetched gamble in the first place, so they had to play really coy so that Hartman would not break his fanaticism to grow wise to their Xanatos Gambit.