The basis of herd immunity is that a person cannot be infected twice by the same virus, so once someone has had the disease it will never happen again. But this assumption has not been proven.
People have a natural tendency to seek balance, and most of us would rather stand aside from a conflict than jump into it. One way to do that is to choose not to take sides. Sometimes that’s the right thing to do, sometimes it isn’t.
There are issues related to Donald Trump’s presidency which are not in any way political, and which define the more fundamental divide between those who follow him and those who do not.