This doesn't seem to be a game that tries to be particularly clever--one button could kill you, the other certainly won't. Trusting that nearly everyone will avoid pressing the button that could kill them seems a reasonable assumption, and it's not necessarily an indication of a lack of altruism.
One button means you almost certainly contributed to homicide, since the odds of everyone pressing red is essentially 0%.
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."
One button could kill you — if and only if enough people press the other button.
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.