All the debates we have are internal debates.
We are Westerners. They have three schools of thought in politics. The Left, the Right and the Liberals. These may be compared to a three set Venn Diagram - related but different.
Everything we think is inside the three school paradigm - that is our Western Orthodoxy.
We have got something from the fundamentals right or we wouldn't be, and it's amazing this isn't stated for the bare fact it is more often - the largest and most successful human civilization in human history by every metric there is.
The problem is of course we are likely wrong about something that will prove our undoing. The question is: what are those things?
The natural tendency is to promote our preferred school over the others but this is a weakness. You can imagine the Romans or Chinese looking at their civilization's decline in retrospect - giving their just-so-story of why it happened. In most cases it is going to be blaming the usual suspects aka the failure modes of competing schools and that isn't enough to explain something systematic. I expect that Joesph Tainter's way of thinking is closer to the mark in getting to real answers - which should be possible.
This may not be a specific answer to the question "what will undo us?" but what jumps out at me is how all Westerners presume their school of thought to be a universal as the monotheistic religions have of their beliefs but there is nothing easier than to show Leftist/Rightist/Liberal dogma does not hold relevance in other times and places. Why didn't the Greeks invent the Industrial Revolution? Maybe they weren't looking for the kinds of answers that would have taken them to new forms of energy and transport because they placed importance on other things.