It is fascinating isn't it? I think that she is a performance artist in the truest sense of the term. She was quite literally prepared to die for her art; extremely brave, I know I couldn't do it.
Like you say, experiments like this really expose our base, primal, and dark instincts. However they also reveal why we've made it thus far; not everyone decided to abuse Mariana, there were helpers there as well as abusers.
Also Zimbudo's girlfriend effectively stopped the Stanford experiment by walking out.
We are incredibly complex social creatures, with undeniable ties to our savage past, which is what makes these things so fascinating I guess.
Thanks for stopping by!