That’s maybe too flippant. “This is fake” is a way someone can rationalize doing something that they know is wrong. It’s important that they came up with that idea themselves, in response to a seemly inappropriate demand from an authority.
Notice:
The most common explanation was that they believed the person they’d given the electric shocks to (the “learner”) hadn’t really been harmed. Seventy-two per cent of obedient participants made this kind of claim at least once, such as “If it was that serious you woulda stopped me” and “I just figured that somebody had let him out“.
It doesn’t seem that there was anything evident in the room to make participants believe that it was anything besides what it appeared to be. They’re not saying “the screams were obviously acted.” Not “I could see that the box wasn’t connected to anything.” Definitely not “the experimenter told me it was staged.”
What led them to that belief was the social and cultural context. They believed the experiment was fake primarily because they believed that the authority figure would not make or let them actually harm someone. They transferred responsibility for their own actions to the authority figure; “I knew it was fake” is merely the mechanism.
At least, that’s a coherent theory we could put together based on the evidence. If Milgram had sneakily passed participants a note under the table, it would be a foregone conclusion that participants would believe it was fake, the evidence collected would therefore be meaningless, and the experiment generally worthless. That’s why this allegation is so damning to Zimbardo’s project.