I don’t know how an entire civilization can become “incoherent,” though I’m sure there are examples.
This comment has been rattling around in my head for a few days now.
I’m sure there are sociologists and political scientists who have made a study of this and could give us a number, but my guess is that it takes a surprisingly small percentage of a population to foster a critical mass of “incoherence”.
The entire civilization doesn’t become incoherent. But if enough of it does, the whole thing falls down.
This is a big part of why I tend toward the way of thinking that I have. My sense is that civilization is far more fragile than we realize.