Gon is clearly a psychopath, this is out of question. He was already completely used to death and murder by the time he left the island, he doesn't love neither of his parents and pretends to love his aunt because he feels like he owes her. Togashi tries to hide it by pretending that Gon is just a simple kid, but in fact he lacks development because he can't feel anything for anyone outside his little psycho sphere.
He's so love-struck with Killua because they're so alike, but in fact it works just like Togashi wanted it, for they are opposites. Killua tries his best not to be a cold blooded murderer, while Gon just goes down and down that path. His mask fell off completely during chimera ant, where he used a "close friend" (someone he only barely knew) as an excuse to brutally murder an ant who won a fair fight.
Gon is the result of a child without parents raised in the wild. We expect Tarzan, but in reality it's monsters like Gon, without a shred of empathy for humanity, that are born.
He obviously wasn't expecting to get out of there alive. He was willing to use "everything" after all, since he knew there was nothing left for him. The seeds of his insanity coming to light began in the Greed Island arc where he sacrificed both of his arms and had his windpipe crushed not because he was helping out his friends but it was because his pride was slighted. He is VERY self-conscious about how he stands strength wise compared to other characters and Pitou's actions forced him to face that reality. It pushed him over the edge.
He sacrificed himself that time, next time he'll sacrifice himself. Gon is the one walking down the path of darkness not Killua.
And then you have the most terrifying fact, he's not upset because Kite is dead but because he feels guilty.
Do you think his suicidal mission is justifiable? I'm expecting some good arguments from you specifically @
Bep07Law