The other one does not contribute to homicide.
The right answer, by the way, is to not press either button. "The only winning move is not to play."
There's a cruise ship that needs to have a certain weight in order to not capsize. That weight threshold happens to be at 50% of the population (for whatever population we're considering in the original question). If the ship capsizes, everyone on it dies.
You're given the option: either get on the cruise ship or don't. Not to take an actual cruise, not for some other intrinsic prize, just file on it for a minute and then get off.
I don't see how those who refuse the risk of dying on the ship are complicit in the deaths of those who willingly choose to hop on it knowing the risks involved
If a rigid airship is being blown about, and might be unmoored, a trained ground crew will jump on the lines because with enough weight they can save the ship and its crew. If too few grab a line, it will unmoor. If you are on the ground crew, and you let go of the line because you are worried about your own life, are you complicit in the deaths caused by the ensuing airship crash?
The other button certainly won’t kill you, but will kill everyone who pressed the first button — if and only if enough people besides you press it.