Well, you all are obviously quite brilliant, but I think Red John is an idea
before I start, I am going to tell you that I am an Asian, so you would expect bad grammars and vocabulary
I think Red John is an idea which delivered by the 1st killer since 1998. It's an idea for those who have unhappy childhood or abused ...it's the way to let them feel safe and protected. As soon as the 1st killer did this, he quickly stole others people's attention, then another person appears and take this " responsibility".
Just Like Batman, It's a symbol of Justice and Fear...Red John can be a symbol of Injustice. Red John can be few people which shares the same identity to kill.
(This is just my personal Opinion)