Having impulsively, it is probable, and perhaps somewhat prematurely revealed the prime but private purpose of the Pequod’s voyage, Ahab was now entirely conscious that, in so doing, he had indirectly laid himself open to the unanswerable charge of usurpation; and with perfect impunity, both moral and legal, his crew if so disposed, and to that end competent, could refuse all further obedience to him, and even violently wrest from him the command.
There are no more uses of "impunity" in the book.
Show samples from other sources
I must not only punish, but punish with impunity.
Edgar Allan Poe -- The Cask of Amontillado
They spoke of eternal youth enjoyed outside the confines of loops, of jumping back and forth from future to past with impunity, suffering none of the ill effects that have always prevented such recklessness—in other words, of mastering time without being mastered by death.
Ransom Riggs -- Miss Peregrine’s Home for Peculiar Children