How did General Zaroff justify or explain the reasons for inventing his new type of hunting?

During his first dinner with Rainsford, General Zaroff elaborates on his affinity for hunting and discusses his exploits hunting dangerous, exotic animals from around the world. Zaroff then mentions that he became bored hunting animals because they could only rely upon their natural instincts, which were no match for his intellect. After contemplating his issue, Zaroff decided that he needed to hunt a quarry that could reason and match his wits. He then purchased Ship-Trap Island, where he began to hunt humans. Zaroff's confession appalls Rainsford, who calls him a murderer. Zaroff responds by saying that he is surprised that Rainsford holds such naive, "mid-Victorian" views regarding the value of human life. The general then justifies his actions by telling Rainsford,

Life is for the strong, to be lived by the strong, and, if needs be, taken by the strong. The weak of the world were put here to give the strong pleasure. (Connell, 8)

Ironically, the general's justification for hunting humans on his secluded island corresponds to Rainsford's earlier comments to Whitney about the world being made up of two classes, "the hunters and the huntees." Essentially, General Zaroff feels that he is justified for murdering weaker humans because he is stronger than them. It seems he genuinely believes that "inferior" people were put on the earth to give him pleasure.

One evening at dinner, General Zaroff intrigues Rainsford by telling him that he's found a new kind of quarry, one that provides him with the most exciting hunting you can possibly imagine. This animal is a true match for Zaroff's wits: it's courageous, cunning, and—above all else—has the capacity for reason. Much to Rainsford's horror, he discovers that the animal Zaroff is referring to is man.
Rainsford immediately puts Zaroff in his place, telling him that this particular kind of hunting is nothing more than cold-blooded murder. But Zaroff simply finds Rainsford's objections amusing. He goes on to attempt to justify his murderous new hobby, arguing that life is for the strong, and that the weak were put on this earth to give the strong pleasure. As Zaroff regards himself as one of the strong, he thinks that this gives him the right to hunt those he deems to be weak and inferior.