Was it Rainford's adversion to hunting humans? And in the end he became the hunter? Kill or be killed? Maybe when someone is put in a life or death situation either they choose to give up and hold on to their values or they may choose to put them aside and defend their life?
In addition to humans indulging in their thirst for violence, the violence is gratuitis in that it is only perpetrated for the individuals pleasure. Both Zaroff and Rainsford hunted for pleasure. If Rainsford ever hunted because he needed the meat, we don't know about it because it was never revealed.
Totally agree with all previous posters. I would add a bit about the perspective of Rainsford in all this. In the beginning he's rather smug, saying there were two kinds of people--hunters and the hunted. His implication is clear in a couple of senses, First of all, hunters are superior. He sees those who allow themselves to be hunted as somehow weak and inferior. Second, he is a hunter. How ironic, then, that Rainsford ends up being the thing he showed such disdain for; he became the hunted. The lesson is implicit in this reversal--treat others with dignity and respect whether you see yourself as superior or not, because circumstances change and it might one day be you in the weak and vulnerable position.
First, I believe that Connell wrote the story mainly to entertain. His use of suspense and irony with little thematic or character development lends itself to that conclusion. However, through the opening dialogue between Rainsford and Whitney, the reader can infer that Connell will comment on fear and its effect upon humans. Your third question addresses this. Of what is a human being capable when he/she faces fear?
Additionally, the story's setting is significant to one of Connell's points. Zaroff uses an exotic island to practice his maniachal game because he knows that it is socially unacceptable. While the general does not seem to care what others think about him or about damning his soul, he wants to be able to live without the constraints of society. Connell, much like Golding in The Lord of the Flies, chooses an island setting to illustrate what happens to mankind when he is removed from society. Connell's view seems to be very similar to Golding's--those who want power take over and are either corrupted by their power or wanted power in the first place in order to do whatever they please. Both authors demonstrate a faith in the dark side of human nature, especially when social restraints are absent.
Connell was demonstrating via General Zaroff the lengths to which humans will go to indulge their thirst for violence and cruelty. The author also illustrated how horrendous crimes appear to lose their horror for the perpetrator when he who commits them is of high socioeconomic status. Zaroff's wealth has removed him, in his own mind, from the immediate awfulness of the multiple murders he is responsible for committing.
I think all of your answers are valid, actually, I think the whole notion of critiquing the practice and mentality of hunting is quite valid. I also believe that your discussion of philosophy of action when one's life is jeopardy is also a valid point. I cannot help but think that there is a social dimension present. Connell writes this in the 1930s (I think it is 1932 or something like that.) America is in the midst of the Great Depression, and the vision of the Jazz Age and the 1920's emergence of the celebrity life and lifestyle seems like a distant vision. There might be some type of connection between those who believe in their own infallibility and superiority can face challenges which cause reevaluation of such claims. Certainly, Rainsford believes in his own mortality and is humbled after seeing Zaroff's savagery. I think that some social statement is being made about where America was at the time (the 1930s) and from where it emerged (the 1920s.)