You can't really be this silly. You can't ethically study this shit, it would need two groups, a control group that doesn't get desensitized by the horrible things the other group does to people. But you can personally observe the changes in people of places of authority and stress over time. There's maybe a few studies in the past, like the Stanford one, Milgram I think, that ethicists discourage.
The Stanford prison experiment was faked mate. Guards were told to act cruel and the results were pre-written.
Biological truths such as 'x causes y in humans' needs to be backed up by some very serious science, a few choice studies from the 60s barely scratch the surface of that. Because there are a million influencing factors in each and everyone's life that can drastically change the way we respond to events.