Is it a fallacy to say that a sane person cannot apply rational thought to the motivations of the insane?
A common argument in today's news is that: 1. Someone commits a heinous crime by shooting a bunch of people. 2. Anyone who commits a heinous crime must be insane. 3. Sane people cannot apply rational thought to explain what motivates the insane. 4. Therefore, one cannot ascribe a cause or catalyst to a heinous crime. Is there a fallacy in this logic? If so, what is it?