[Link warnings: most of the links in this post go to sites that contain graphic images of human death, experimentation, and humiliation. Click at your own discretion.]
Over at Listverse, they have a post about the top 10 evil human experiments, and I agree that this list is horrifying, if educational. I’d already done my own studies in the Stanford Prison experiment (at #10), but some of these experiments left me with chills. As was mentioned in a prior comment, I suspect it has something to do with people thinking that they have the right because they’re either convinced of their own superiority, convinced that because it’s in the name of science that it must be justified, or for some other, more obscure reason.
As you might have noticed by now (and by some of the posts I put up), I’m both fascinated and appalled by what people are willing to do to each other, and I suppose that my fascination is me trying to make sense of it: what are their justifications? How do they feel about it afterwards? Where do these justifications come from? In at least two famous cases [Case 1: Milgram Experiment, Case 2: Hofling Experiment, both at Wikipedia], the justification came about because “I was told to by some authority”. It certainly boggles the mind that people are willing to abdicate responsibility and common sense because a perceived authority told them to.
And sadly, in the cases of these experiments, much like several horrific massacres (all Wiki links) that took place, maybe it was a combination of authority abdication and that the people being slaughtered were just not seen as human anymore.