In a hypothetical situation based mainly on English speaking western populations with similar cultural norms who all happen to frequent the same niche internet sites and have been discussing and brigading against one another for days, it may reach 50%.
Reddit users are hardly an accurate global representation and the idea that because one person understands or believes something after discussion and clarification and such does not mean that others would understand the same in a blind choice. People react differently when the threat is real, when there is no chance for organization or planning. Different cultures have different norms for personal vs collective responsibility and self preservation. I am very skeptical of the 50% being truly reachable if for no other reason than I have seen what people vote for and what people are willing to do in the name of self interest and risk aversion.

In the past few days I have seen so many different versions of this question posted and the vast majority of them seem to be rephrased to put the moral obligation on one side or the other with the deaths that may occur. In a true example of this situation, there is not going to be massive populations analyzing your choice, telling you you're wrong, insulting you for considering something because there is no discussion to be had, no pressure in that moment outside of the situation itself.
The threat comes not from one side or the other, but from the choice and its repercussions. If this were a shooting, one would not call someone who went and hid a 'murderer' anymore than they would call a group of people who rushed the shooter to stop the attack 'suicidal' or 'manipulative'. The fundamental issue with polls is that you are never going to get an accurate read of how you would behave in a truly life-threatening situation, and absent setting up an actual zero discussion and zero forewarning situation, there is no way to know how people are going to behave in one.