I am proposing no such thing. From the reports of the captain's actions on the aircraft it should be apparent to anyone that here was a tortured soul who finally "went off the deep end", so to speak. His snapping did not happen overnight.
There was probably a progression of events within his mind, apparently noticed by no one, that led to this.
The problem I have is with some who, not knowing the underlying causes, simply label a person "criminal" when the intent of that person was anything but criminal. Perhaps in the captain's mind he really believed something which those of us who are considered "normal", scoff at. I have known a few people who are medicated schizophrenics. They are fine. Until they miss one of their doses. Then, the voices in the head start. And they really do believe someone is talking to their mind. For the observer, it's a very eerie experience.
For the victim, it is real. And if that voice in the head tells you that maybe it's a good idea to take that airplane you're flying down, then you do so. Regardless of the outcome.