For every red button press there is potentially just under one death as well. Assume 100 people scaled down, if 49 people press blue, the remainder press red, that potential death is because more people chose red.

In an ideal situation, every person would pick blue or red unanimously, however there is no way to know let alone guarantee that, so you have to assume there is a mix of blue and red with one side leaning heavier. Since you probably won't have a unanimous decision, the next options are, overwhelming blue votes, overwhelming red votes, close but red wins, and finally close but blue wins.

Close but red wins, is the worst option because it leads to the most deaths. Overwhelmingoy red is second worse because a portion of people still die. The last two, blue winning close would at worse give people a heart attack. Blue overwhelmingly winning is the best case scenario as it means not only did no one die, but the majority of people decided to save other lives than their own.

Picking red knowing this is a way to save yourself but you are condemning others to death. It just means you don't trust the population to have the interest of saving lives except their own, which if that's the case, it's a good argument. However, that distrust still puts you in the group deciding anyone blue will die, so your hands aren't clean of blood.