Is it a fallacy to say that a sane person cannot apply rational thought to the motivations of the insane?

Question

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?

Answer 1

There are a few problems I feel with each of the points individually, but in short I feel the main problem is the relationship between "motivates" and "cause " (point 3 and 4). Assuming we cannot comprehend of even fathom anything about the thought process of the insane, we can still observe, I.E. stimulate and observe reactions.

For example, I may not know what "motivation" an insane dog has to bite me after I kick it (I.E. probably anger or self defense but let's assume it's "insane" and thus we can't assume or postulate any type of mental/emotional stimulus) I can however ascertain reasonably that the cause of the dog biting me was me kicking it.

Unrelated side note: one of my favorite Robin Williams quotes is "we all have a spark of madness in us, we mustn't lose it." so maybe we all have a slight ability to understand even the "mad" or "insane".