Gon and Killua acknowledged that Greed Island is a game where it is implicit that you will be putting your life on the line. When you come into that game, you expect that you will be confronted with life or death situations. Killua contrasted that to the assassinations he performed in which his victims were not expecting to die or willing to put their lives on the line. Also, take into account Gon's attitude towards people trying to kill him. He does not hold it against his opponent. Gon's only anger issues with Genthru in that fight was that Genthru refused to use his ability initially, and that he went back on his word. Otherwise, his attitude towards Genthru would be more like "Well, if we fight, one of us may die. This is the nature of fighting, no hard feelings. But in the case I win yet you live, I will heal you. that's just who I am."
Also, last time I watched this, I didn't realize how close Gon came to winning that fight without resorting to the plan. Genthru got lucky in that he tripped over the rock and avoided the attack.
"You are not free whose liberty is won by the rigour of other, more righteous souls. Your are merely protected. Your freedom is parasitic, you suck the honourable man dry and offer nothing in return. You who have enjoyed freedom, who have done nothing to earn it, your time has come. This time you will stand alone and fight for yourselves. Now you will pay for your freedom in the currency of honest toil and human blood."
- Inquisitor Czevak
Yeah I think that's the best way to put it.
Im not saying they're different, I am agreeing Gon doesn't approve of murder.
Did you watch the beginning of the arc? After hearing about the bomber Gon was blatantly upset that someone had turned his father's game into a killing competition. Its a little different than risking your life fighting the monsters and events.
I feel like maybe that was his feelings only in the beginning when he didn't actually know any better. Round about the time he was fighting Razor in a game of Deathball he probably realized that "Oh, dad hired Death Row inmates to kill anyone that tries to actually win this game, I guess he really DID design this place as a giant murder machine."