WILLARD: "Never get out of the boat." Absolutely goddamn right! Unless you were goin' all the way... Kurtz got off the boat. He split from the whole f***in' program.
Willard seems to be saying that once you've abandoned the plans the army's laid out for you, you're at risk for becoming seriously unhinged. Once you've left the metaphorical boat, you're in the lawless jungle.
KURTZ: I watched a snail crawl along the edge of a straight razor. That's my dream; that's my nightmare. Crawling, slithering, along the edge of a straight razor...and surviving.
For Kurtz, reality boils down to that raw struggle for survival—it's both his dream and his nightmare. You have to live on the thin edge between life and death. Ugh—once you've imagined that snail, you can't un-imagine it.
LANCE: You know that last tab of acid I was saving? I dropped it.
Here's how one commentator described Lance's drug use: "This may be camouflage more than anything; while sanity would stand out against this background, insanity blends right in" (source).
WILLARD: (reading) "There has been a new development regarding your mission which we must now communicate to you. Months ago a man was ordered on a mission which was identical to yours. We have reason to believe that he is now operating with Kurtz. Saigon was carrying him MIA for his family's sake. They assumed he was dead. Then they intercepted a letter he tried to send his wife: SELL THE HOUSE. SELL THE CAR. SELL THE KIDS. FIND SOMEONE ELSE. FORGET IT. I'M NEVER COMING BACK. FORGET IT."
Captain Richard Colby—he was with Kurtz.
Captain Colby's apparently drunk the Kool-Aid. He saw something in the jungle and in Kurtz that made him throw his life away. When Willard sees the man he assumes is Colby, he looks emotionally dead, expressionless. He looks just like the kind of man Kurtz wants: one who can kill without emotion or judgment.
WILLARD: Could we, uh...talk to Colonel Kurtz?
PHOTOJOURNALIST: Hey, man, you don't talk to the Colonel. You listen to him. The man's enlarged my mind. He's a poet warrior in the classic sense. I mean sometimes he'll...uh...well, you'll say "hello" to him, right? And he'll just walk right by you. He won't even notice you. And suddenly he'll grab you, and he'll throw you in a corner, and he'll say, "Do you know that 'if' is the middle word in life? 'If you can keep your head when all about you are losing theirs and blaming it on you, if you can trust yourself when all men doubt you' ...I mean I'm...no, I can't...I'm a little man, I'm a little man, he's...he's a great man! 'I should have been a pair of ragged claws scuttling across floors of silent seas...'"
We're guessing that this babbling photojournalist is pretty hopped up on some kind of jungle pharmaceuticals, but being a witness to Kurtz's brutal little community in the jungle probably hasn't helped much. The lines beginning with "If you can keep your head" and "I should have been a pair of ragged claws" are from Rudyard Kipling's "If" and T.S. Eliot's "The Love Song of J. Alfred Prufrock," respectively. As we learn, Kurtz is a huge poetry fan.
WILLARD: They told me that you had gone totally insane, and that your methods were unsound.
KURTZ: Are my methods unsound?
WILLARD: I don't see any method at all, sir.
Kurtz has gone off the deep end, into a world where there are no rules. Just the rein of brutality and ruthlessness. Or has he? This is one of the film's central questions. Kurtz's actions seem completely unhinged, but he has a very clear idea of why he's doing what he's doing. Willard sees no method, but Kurtz later lays it out in detail.
PHOTOJOURNALIST: I wish I had words, man. I wish I had words...I can tell ya something like the other day he wanted to kill me. Somethin' like that...
WILLARD: Why'd he wanna kill you?
PHOTOJOURNALIST: Because I took his picture. He said "If you take my picture again, I'm gonna kill you." And he meant it.
Why doesn't Kurtz want his picture taken? Is he buying into a superstition of the Montagnards who follow him? Or is it that he doesn't want his current degraded state to be witnessed by the world?
PHOTOJOURNALIST: The heads. You're looking at the heads. Sometimes he goes too far. He's the first one to admit it.
The film is teasing us again. Kurtz does crazy things, but he knows they're pretty extreme. If he were really crazy, would he have that ability to reflect and judge his actions? On the other hand, if you displayed some chopped-off heads once and regretted it, we'd think you probably wouldn't do it again.
PHOTOJOURNALIST: Why would a nice guy like you want to kill a genius? Why? Because they told you he was crazy? The Colonel is not crazy. The man is clear in his mind, but his soul is mad.
The journalist says that the Colonel is clear in his mind because he really does think extreme brutality is necessary to win the war. But his soul is mad, because at some level Kurtz is horrified by what he's doing. In Heart of Darkness, Conrad wrote: "I saw the inconceivable mystery of a soul that knew no restraint, no faith, and no fear, yet struggling blindly with itself." That struggle seems to be why Kurtz almost welcomed Willard to kill him. He knew what he had to do to win, but couldn't take it any longer.