[Rakshasa]

As the instigator of this thread, I find the answers somewhat dissatisfactory. Likely the compounding of a game world with RL consequences muddles the waters, so let's look at a hypothetical situation.

If Kayaba had locked up 100 people in a large cavern with enough food, water and facilities to survive, and some unclear objective that was required to reach in order to be released. Each has a couple of devices around their neck and affixed to their right hand, the former kills them if they fail some task on the way to clearing the objective, or just at random if they don't do anything, and the latter is a gun of some sort.

They cannot remove either without losing their heads.

Now it is obvious that Kayaba would be criminally responsible for every single death no matter what, however what would happen if someone started using the gun to shoot other people?

An insanity plea could be used in most modern democracies as a valid defence, however it isn't normally enough to just say the stress of imminent death got too much to handle. What one looks for is a real loss of understanding of what is real and not, not merely acting upon frustration and rage.