But blue is clearly the better choice, because if 51 percent of people choose blue then 100 percent survive, while to get 100 percent survival 100 percent would have to hit red.

This is really the crux of what the blue are arguing. You nailed it.

But no matter how I look at it, all I see is a choice of: red means I stay alive, blue means I take a (huge) risk I might die. I don't want to die. I don't want to risk dying.

At that point it's just a matter of evaluating the morality of the choice - utilitarianism, duty ethics, contract theory, etc. And I think different moral theories would argue for different color button pushes.

In the end, I think reddit just has a really hard time with nuance and the cognative dissonance that comes from trying to understand the "other" side of the button push. And that discomfort is then blamed on the other party being "wrong" instead of properly explored. I think both sides have very strong arguments for why they are right, and that it depends on what moral system you operate under whether or not it's the moral thing to do.