Healthy animals kill each other leave much of the carcass behind all the time-— not to mention the fact that they play with their prey. Just watch a housecat around a mouse.
I doubt what you say about serial killers is correct. If it was, the number of serial killers would have been greatest in societies where children hunt for fun in addition to any other reasons—— yet the number of serial killers has grown while the practice of hunting, for fun or whatever other reason, has not.
You might have had a point if you changed “hunting” to “torturing”-— John Stuart Mill thought so. While I doubt Mill had any empirical evidence to that effect, either, I would distinguish hunting from, say, dog fighting such as Michael Vick is suspected of promoting. Hunting keeps the worlds of human and animal separate, so that the confusion you speak of is unlikely, whereas people who raise animals as pets only to mistreat them are closer in psychological terms to mistreating a member of his or her family.
Do you really believe I wrote that serial killers get their start by hunting?