Here are several scenarios that are functionally identical to the buttons.
REMINDER: THERE ARE NO BABIES
Green Aliens show up with disintegration rays. The rays affect every human they identify simultaneously, with no delays or gaps. At the same time, Purple Aliens send out a broadcast and tell everyone that the rays have to be seen by a human eyeball to be effective. The Purple Aliens tell everyone that if everyone just closes their eyes, they'll be completely unaffected while the Purples arrest and remove the Greens. They also tell you that if more than 50% of the people keep their eyes open, it will overload the disintegration rays, and the people who kept their eyes open will only get a mild eye irritation that will clear up in a couple of hours. Do you keep your eyes open or do you close them?
A large building is slowly falling toward a group of people. The people are told that they have two choices: They can move out of the way of the falling building and completely avoid getting hurt. Alternatively, people can band together and put their hands up to stop the building from crushing people - but that will only be effective if more than half the people work together to hold up the building. Do you try to hold up the building, or do you move out of the way?
Everyone is magically given a copper fork and presented with a lump of clay and an electrical outlet. An announcement is made that each person has a choice of sticking their fork into the clay or into the outlet. The outlet is live, and has a fatal amperage... unless more than half of the people stick their forks in the outlet. If more than half stick their forks in the outlet, it will short the circuit and nobody will be harmed. Do you stick your fork in the outlet or in the clay?
There's a large vat of poison, which will be divided evenly between everyone who chooses to drink some. If more than 50% of the people choose to drink poison, it will make everyone feel icky but nobody will die. If less than 50% choose to drink poison, it will kill everyone who drinks it. Water is available as an alternative. Do you choose to drink water or to drink poison?