Wolf Larsen, being partially inspired by nihilism, believes that life has no greater purpose than its own survival. He sees nothing on the horizon except the present moment; he cares nothing for the future or for the greater impact of his actions. Instead, his entire worldview is based on his personal survival, pleasure, and ability. His body is powerful, and he believes that this is the random chance of biology, giving him the better ability -- and therefore the better right -- to impress his will on others.
"[Life] is like yeast, a ferment, a thing that moves and may move for a minute, an hour, a year, or a hundred years, but that in the end will cease to move. The big eat the little that they may continue to move, the strong eat the weak that they may retain their strength. The lucky eat the most and move the longest, that is all. What do you make of those things?"
(London, The Sea-Wolf, gutenberg.org)
In Wolf's view, his size, intellect, and strength are enough to justify his actions; he is stronger and so he is allowed to prey on the weak because there is no larger purpose. In this way, he acts entirely without conscience; without the philosophical ability to "care" about others, he has no compassion at all. In this way, he can be compared to General Zaroff, the antagonist of Connell's "The Most Dangerous Game," who hunted weaker men for sport, with similar justifications.