If you press the red button, you live, but if you press the blue button, you die unless 51 percent of people press the blue button.

It's true that if everybody presses the blue button, everybody also lives. But blue-button folks are putting themselves in danger by gambling that enough people are also going to take the risky option. That is a very bad bet. Red-button pushers are guaranteeing their own safety, at zero cost to anyone else.

Hope that helps.