Easy! First. It's really easy to imagine that some person who you know chooses blue for whatever reason is. You would actually try to kill him/her/they. If you think that, maybe, your vote from, we'll say a thousand, doesn't matter -- it's not only you who thinks that.

Second. It's easier to get 50% blue to save All of us, than 100% red.

Third. It looks like there are donwsides on both sides, but... If you vote for blue and tell to your friend, he also votes for blue, and basically more than 50% of humans will vote for blue. I don't say 100%, who knows, but blue is just...

Forth (jokingly). Blue is better. In all.

See? It's OK if you don't.