There is a very real difference between a hypothetical thought experiment with no actual consequences and a real world scenario where one is facing the possibility of death if enough others don't join in.
Keep in mind that in the experiment, the vote is private and anonymous. You have no idea who or how many others are picking which button to press. So imagine that who or whatever that is running this test shows up in front of every living person and attaches a collar on your neck with a bomb attached. Red, you live no matter what, the collar comes off. Blue, and you have to hope that 50% 1 all select that button.
The scenario hasn't changed in this situation, it's just that the threat becomes real.
The tension is there. Now you have to think about it. You now have to overcome the very basic human instincts of survival and self-preservation. Moreover, you need to account for cultural differences where in some countries, survival is something they deal with as a daily part of life - and would never press the blue button to begin with.
Red button pressers are not hoping for a purge. Red button pressers basically fall into one of two categories.
The first one (and likely the majority) are motivated by fear, feel helpless to do anything else and just want to live.
The second one is the rational red button presser. It's the one that understands some will die. The rational one does the math and understands that the 50% threshold will never be met on the blue side and knowing this, hopes that as many as possible press red so that people will live.
It's very difficult to overcome human nature, and I think most of the blue button pressers who answered that on social media will quickly choose red when faced with the very real possibility of death. At the end of the day, I imagine the percentage of intentional blue button pushers would be very low.
If you want an example of this in real life, think of the bystander effect. Those that don't intervene to stop a crisis are preserving themselves - they press the red button. Those that do intervene are the blue button pressers, putting themselves at risk for another.
Whether it's a public murder, school bullying, workplace harassment, a mass shooting event, or anything else you can think of, where a mass of people are involved, few are willing to step in.
When death is on the line, I think this is only enhanced further. "I won't press blue, but surely others will and enough will do it." And almost all the would-be blue button pushers would press red as a result.
That's the reality. That's why millions and billions never press blue. Not everyone will press red, but almost everyone will.
Everyone on earth takes a private vote by pressing a red or blue button. If more than 50% of people press the blue button, everyone survives. If less than 50% of people press the blue button, only people who pressed the red button survive. Which button would you press? BE HONEST.