Sure they are, but the layer beyond that is that they wanted to test the boundaries. She told them anything goes, which means on some level she wanted the freaky shit, and participants didn't want to disappoint.
Absolutely. The number of people in the comments who have missed the whole point of this piece is staggering.
It's performative endurance art. Marina was very much hoping and intending to make a statement on the human condition and the flexible limits of our morality. The audience played their part perfectly.
I know that some of you are outraged at the whole thing, but remember that art can't hurt you, the viewer. Art is supposed to make you feel things. And subsequently, you should have sufficient emotional intelligence to analyse and challenge those emotions and the ethical and moral preconceptions they stem from.