Sickening. But this quote rings quite true:

Yeah, this is essentially Stanley Milgram's obedience experiment for the 21's century. The explicit intent of the art piece isn't to starve the dog to death, but to expose the blindly obedient nature of the gallery goers. That doesn't excuse it, as this experiment was already done...by Stanley Milgram. As I recall, a life was lost during that experiment, only it was a human who committed suicide, having been so horrified that he / she could be led to do something like that.

Still sick, and shame on the art gallery visitors.
I was thinking something along the same lines (obedience to authority and "pack mentality").