If Damon knows enough about education policy to speak at a rally, then he knows enough to take a meeting with Arne Duncan and debate it. Getting a chance to make your case to policy makers is what political activists are supposed to want. That's the goal. If Damon feels he doesn't know enough about the issue to survive a meeting with Duncan with his convictions intact, then he has no business speaking at a rally.
First, just making the case to Duncan isn't going to do any good, any more than having an opportunity to bend Paul Ryan's ear on taxes would. It isn't like Damon was speaking on behalf of an unknown new disease or emerging environmental problem; Duncan knows the arguments.
But more than that, we all know Duncan's approach would probably be to pretend to agree with Damon. He's very happy to act as if he is against the unpopular aspects and implications of his own policies.