> if Bentham becomes an agent that goes for C, he also explicitly discourages the mugger
How is this different from saying that if Bentham decides to not adhere to utilitarianism, he is no longer vulnerable to such a mugging? If Bentham always responds C, even when actually confronted with such a scenario (the mugger was not deterred by Bentham's claim), then Bentham is not a utilitarianist.
In other words, the GP is saying: "if Bentham doesn't always maximize the good, he is no longer subject to an agent who can abuse people who always maximize the good." But that is exactly the point -- that utilitarianism is uniquely vulnerable in this manner.
How is this different from saying that if Bentham decides to not adhere to utilitarianism, he is no longer vulnerable to such a mugging? If Bentham always responds C, even when actually confronted with such a scenario (the mugger was not deterred by Bentham's claim), then Bentham is not a utilitarianist.
In other words, the GP is saying: "if Bentham doesn't always maximize the good, he is no longer subject to an agent who can abuse people who always maximize the good." But that is exactly the point -- that utilitarianism is uniquely vulnerable in this manner.