Perhaps you weren't aware, but Eliezer has stated that it's rational to not respond to threats of blackmail.

I'm also pretty sure it's irrational to ignore such things when making decisions. Perhaps not in a game theory sense, but absolutely in the practical life-theory sense.

As an example, our entire legal system is based on these sorts of credible threats.

To be precise, not respond when whether or not one is 'blackmailed' is counterfactually dependent on whether one would respond, which isn't the case with the law. (Of course, there are unresolved problems with who 'moves first', etc.)