Pushing red guarantees survival.

This is not just a matter of individual survival, either. It's also a matter in which "calculus of least harm" ethics dictates the choice. Because it's simple to figure out that pushing red guarantees a person's individual safety, human nature dictates that the overwhelming number of people who figure that out will push red. This number will be a near-certain majority, since as I said, the choice's ramifications are simple to figure out. There is virtually no chance that blue will be the majority. Thus the "least harm" scenario that actually has some likelihood of occurring is for as many people to choose red as possible, reducing the number of dead.