<<It is much less true for the mentally ill, who have a twilight of recognition, often, from going about their daily lives and noticing not only how they feel but also how people react to them. There was plenty of the latter in Cho's life. I maintain that it's a very bad precedent to divorce responsibility from the actor himself except in the most extreme circumstances. Indeed, that is presently and will remain for quite some time the stance of U.S. law.>>
There are certain actions, like taking your medication on time, that definitely can serve as a measurement of responsibility or irresponsibility. I'm sure, as you pointed out, there are other situations where responsible preventive action is called for before an individual succumbs to irrationality, warning signs of various natures which can be acted on or ignored depending on one's degree of responsibility. Whether it's only the extremely unfortunate who are unable to respond in time to the warnings, or only the extremely fortunate who can, I don't feel qualified to judge. From a legal perspective, I suppose, you'd want to extend the ambit of responsibility as widely as possible so that more people are caught by the legal imperative to moderate their actions before they become crazy, but I don't know how practical it is to try to assess which minds are capable of making the often subtle distinctions that enable them to recognize the warning signs. When in doubt, I tend to follow the criminal law maxim (because it's really criminal acts that we're talking about) that requires proof beyond reasonable doubt.