There are going to be a lot of people who pick blue thinking it’s the right thing to do. Let’s say at least 20% of people. So in a red wins scenario, you are guaranteed to kill at least 20% of people - and the people who were trying to do the right thing, too.
To get a “no one dies” scenario from pushing red, you need to get EVERY SINGLE PERSON IN THE WORLD to all make the independent decision that red is the right choice. Would never happen. Billions are gonna die if red wins.
However, blue’s route to zero deaths is far easier. You just need to get 50%+1 of the world’s population to get on board, then no one dies. Getting 50%+1 on the same page is a gazillion times more likely than getting 100%.
Red is basically guaranteed hundreds of millions or billions of deaths. Blue is a pretty good chance at 0 deaths.
If you want an exhaustive, more thorough set of arguments than that, the earlier thread has it in detail.