The conflict with Zaroff changed Rainsford from morally opposed to killing into willing to commit murder.
The central conflict in this story is the person versus person conflict between Rainsford and Zaroff. It leads to many internal conflicts in Rainsford. Rainsford’s conflicts involve his fear of Zaroff, his battle with his nerves, and his conflict over whether or not it is okay to kill humans.
At the beginning of the story, Rainsford is a hunter who enjoys hunting and does not ever stop to consider what the animal who is being hunting is feeling.
When Rainsford and Whitney discuss the feelings of the animals, Rainsford does not take the animals's side.
Don't talk rot, Whitney," said Rainsford. "You're a big-game hunter, not a philosopher. Who cares how a jaguar feels?"
"Perhaps the jaguar does," observed Whitney.
"Bah! They've no understanding."
This shows that Rainsford has no problem with the concept of killing, is very good at it and even likes it.
However, when he first learns that General Zaroff hunts human beings, he calls it murder.
“…I'll wager you'll forget your notions when you go hunting with me. You've a genuine new thrill in store for you, Mr. Rainsford."
"Thank you, I'm a hunter, not a murderer."
Rainsford apparently draws the line at hunting human beings. Zaroff calls him old fashioned, but Rainsford refuses to hunt with him, so he has to be the prey.
During the game, Rainsford’s skills are put to the test. It draws on his nerves. He is used to being put in stressful situations. That’s normal for a hunter, and he has also been in World War I. However, this is apparently more dangerous than what he has ever faced.
Rainsford had dug himself in in France when a second's delay meant death. That had been a placid pastime compared to his digging now.
When Rainsford keeps matching wits with Zaroff, and Zaroff toys with him again and again, it wears him down. Part of the problem is that the general seems to be very good, and part of the problem is that Rainsford seems to always be right at the edge of losing.
He stood there, rubbing his injured shoulder, and Rainsford, with fear again gripping his heart, heard the general's mocking laugh ring through the jungle.
Whether the general only just gets away, or stops and goes back, Rainsford feels like his nerves are always fraying. He never knows if his next effort is going to work. He makes traps and weapons, and they always seem to only just miss. One kills a dog, one kills Ivan, and one only wounds Zaroff.
This is why Rainsford finally decides he has had enough. He simply can’t take it anymore.
"Nerve, nerve, nerve!" he panted, as he dashed along. …. Ever nearer drew the hounds. … Twenty feet below him the sea rumbled and hissed. Rainsford hesitated. He heard the hounds. Then he leaped far out into the sea. . .
Zaroff is shocked when Raisford shows up in his house, and asks him how he got there. He is very impressed when he learns that he swam, and tells him that he won the game. Rainsford is either not convinced or not satisfied, and tells him that he is “still a beast at bay.” They fight, and he kills Zaroff. He has become the very thing that he refused to allow. He has become a murderer. Rainsford has no regrets for killing Zaroff.
He had never slept in a better bed, Rainsford decided.
Whether you feel that Rainsford is a murderer, or killed Zaroff in self-defense, depends on your point of view. One way or another, it is clear that the conflict changed Rainsford. He was opposed to killing anything but animals when the story began. At the end of the story he can kill a man and sleep like a baby.