John Stuart Mill’s Answer to the Diminished Capacity Argument

Both in law and in our less formal judgments of others’ actions and our own, we recognize the idea of “diminished capacity”: at the moment of doing the bad thing, not being able to think straight. But there are many things that predictably lead to not being able to think straight: alcohol, too little sleep, titanic anger, strong sexual arousal, etc. Because these predictably affect our judgment, we each bear a responsibility to make sure that at each moment we are either (a) avoiding such states at that moment or (b) set things up–say by prearranging many key things–so as to minimize any harm that might come from distorted judgments in those states. It is appropriate to hold people to account on that responsibility. 

John Stuart Mill alludes to that principle in On Liberty “Chapter V: Applications,” paragraph 6:


It would be too great a burden on freedom to punish people for not (a) avoiding states of impaired judgment if they might well be pursuing strategy (b) of arranging things careful so impaired judgment does no harm. But once someone has committed an offense under impaired judgment, the presumption that they are pursuing strategy (b) cannot be held as strongly.

Stepping back, one can consider the human condition in general as one of impaired judgment. Therefore, along the lines of strategy (b), it is our duty to set up social arrangements so that our impaired judgment causes as little trouble as possible. Foremost among such social arrangements is to avoid giving too much power to any one individual. Dictatorship is like drunkenness without any precautions.