Are commitment mechanisms rational?

A malicious genius is considering whether to dose the dashing protagonist with a toxin. The toxin is known to be invariably fatal unless counteracted, and the malicious genius has the only antidote. The antagonist knows that the protagonist will face a choice: Either open a specific locked box containing, among other things, the antidote - surviving, but furthering the antagonist's wicked plan, or refuse to open the box, dying, and foiling the plan.

We analyze this as an extensive form game: The antagonist has a choice to dose or not to dose. If dose, then protagonist gets a choice, to die or not to die.

If only the protagonist was not so very very rational! Because the protagonist is known to be very very rational, the antagonist knows that the protagonist will choose to live, and thereby further the antagonist's plan.

A commitment mechanism, then, is the protagonist (rationally) sabotaging their rationality before the antagonist has an opportunity to dose. The "irrational revenge circuit" will revenge harm at any cost, even an irrationally high cost. Even antagonists step carefully around people with revenge circuits installed. (Yes, evolution has already installed some of these.)