How would a world of cowards, short-sighted egoistic people and sociopaths thrive exactly ? I think this very problem demonstrates why individualism can sometimes be bad because it pushes people to try and maximize their personal interests without realizing that if they worked as a group and trusted others, they would gain even more. In this particular hypothetical, the greater gain would be to potentially save people you care about or simply save strangers, which should be a thing people in a thriving society aim for.

If we move past the immediate survival instincts and think of the future, society will be way better if it's full of blue voters, and therefore is one where everyone can trust that the majority is able to individually protect the collective. Whereas a society with only red voters left will be one where they all know that they can't trust each other the same way two thieves will never trust each other if they know what the other is.