Pressing blue is an unnecessary risk taken by people willing to risk their lives for people who also do the same.
"I'd feel bad if I pressed Red and someone else died"
If they died, that was their choice to take that risk, but if they died because you pressed Red, they still would have died if you pressed Blue, the difference is now you're also dead.
Everyone in the world has to take 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?