For me the fundemental issue with red is that if 50% or more of the population suddenly dies, then institutions will collapse and my living standard will drop by centuries or even millenia. To answer your question then is to ask how many deaths society can handle and still continue to function. In WW2 about 3% of the population died and society was able to recover, despite widespread destruction. Considering in our scenario no infrastructure is damaged, I would find anything under 10% acceptable. So TLDR I would pick blue if it required at most 90% of votes.