Blue is the only moral and logical choice. If red gets over 50% and you picked it, therefore contributing to the "red" outcome, you are now effectively a murderer. Plus you now get to live in a world where everyone else alive are sociopaths that picked red, where everyone with a conscience is now dead.
You also can't count on everyone picking red, or "if you picked blue, then you voted for suicide".
It's reasonable to assume that, leading to the button press event, the usual low-trust, "every man by himself" types will rally for red, with the usual excuses, where high-trust societies will make it clear that it's your moral duty to pick blue, to get the votes to the 50% threshold and ensure no one dies. Around the world there would be debates nonstop that would permeate every social circle and families. You'd have huge arguments where the typical selfish types would scream at their family members "how dare you say you're going to press blue, do you want to leave your poor mother alone without their only child?", only pushing red-leaning voters more into red and blue-leaning voters more into blue.
Plus, if you look at the possible outcomes:
- Red wins, you picked red: Depending on where you live, a reasonable portion to the large majority of the population is now dead. The ones alive have, by definition, a strong bias towards individualism and noncooperation. It's extremely likely civilisation will collapse. Pick your favourite fictional dystopia and you might have a reasonable chance of it actually coming somewhat real.
- Red wins, you picked blue: You are now dead, but at least you don't have to live in the world above.
- Blue wins, you picked blue: Things carry on as normal and your conscience is safe in knowing that you didn't vote to kill and that over 50% of your fellow humans also didn't vote to kill.
- Blue wins, you picked red: Things carry on as normal, but you now have a guilty conscience, or, if your vote was made public, people around you know you would have killed them to save your skin.
