Post button world
I am not sure if somebody already made this point before or not; but here it is anyways:
My personal choice was always blue. One of the main reasons obviously is the fact I am not THAT attached to life, but most importantly is because I wouldn't be able to live with the guilt, especially when it comes to friends and family members
This made me also consider the worldwide effect of either scenarios, as despite the fact that votes stay anonymous, the results will be very public :
Scenario 1 - majority Blue Button: needs no more than 51% of people to choose blue, everybody survives, and since we can't know who chose red or blue unless they confess, I am pretty positive that humanity will be forever changed, possibly for the better, knowing that majority of people are altruistic will curve the rates of misanthropy and distrust. Obviously it isn't easy to assume what will happen, and the aftermath might not be this ideal, but definitely better than the other scenario.
Scenario 2 - majority Red Button: knowing that it is impossible to get all of humanity to choose, 100% is statistically VERY improbable. For the humanity that will stay, chaos at any degree will ensue almost immediately as a % (millions up to billions) of humanity anywhere between 1% to 49% will be dead immediately, which if at least over 10% will have catastrophic effects on social fabric and infrastructure. Consequently, agregious number of people will possibly die or suffer from the infrastructure failure, violence (due to mistrust and anger), guilt (possibly causing mass sυίcίdes and homίcίdes) and possible dissolution of organizations and societies.
So yeah, I am pretty sure even if you are a red button choser, you probably would rather live through scenario 1 while keeping your secret to yourself rather than scenario 2.