One of my favourite quotes is from The Addams Family movie; "what is normal to the spider is chaos to the fly". To me, this perfectly sums up how we cannot create absolute definitions of terms such as "normal" because it means a different thing to everybody.
This is also the case for the term "insane". Its most common definition is "doing the same thing over and over again, expecting a different result" (this definition has also been misattributed to Albert Einstein). The dictionary definition of "insane" is being "in a state of mind that prevents normal perception, behaviour or social interaction".
Now, with a definition as ambiguous as this one, how can we truly know who or what is insane? Is it not simply an opinion? Moreover, trying to define the word "normal" has been the centre of moral philosophy for decades and since there has never been an agreed upon rule for what is "normal", how can another definition be based upon this one?
In the case of serial killers, there are four types; thrill seeking, mission-orientated, power and control seeking and visionary. Only the last type is actually described as being someone with a serious mental illness such as Schizophrenia. So when you hear about a serial killer and their motives behind what they have done, it is almost our instinct to say "there must be something wrong with them. They must be crazy." But really, with everything within this topic being so relative, who says that your version of "right" is right and another person's is wrong?
Something else we naturally do when confronted with the topic of serial killers is assume they have had a poor upbringing, that they were abused as a child or witness to abuse. While this is true for many serial killers, it is not a cause and effect relationship. Otherwise, every single person who had ever been abused would end up as a serial killer. This means that one cannot "blame" the actions of a serial killer on their past. Nor can they say that they are crazy because of their past and how they dealt with it - otherwise again everyone with this past would be classed as crazy.
In doing my research on serial killers for this novel, I found that it is more likely that people will think that someone with a "reason" (such as a bad upbringing) for being a serial killer is actually "sane", since you can understand why they may have gone down that path. On the contrary, the serial killers who have no history of trauma and simply kill because they want to, well these are the ones people can't wrap their heads around and the ones who are assumed to be crazy. When in actually fact these are the ones who fit every societal definition of "normal" apart from in this one aspect of their life.
So what am I saying? I am not saying that what serial killers do is "right". I am not saying I agree with it or think it is "justified". I am simply saying that it is not not right. Who has the authority to say what is? Who are you to judge?