I'm not sure I have an answer to any of the questions, but I do have an observation followed by a question of my own.
Observation: There seems to have always been on "the left" a tendency to connect failure to error, defeat to weakness. But this seems prima facie nonsense, except on religious grounds, or on one of the core principles of capitalist thought, the Doctrine of Progress. After all, we *know*, at two levels, that defeat is certain: at the individual level, we all die. At the level of the species, even if solar power saves the ecology temporarily, at some point the sun will go out. The potential causes of defeat and failure in any given instance, small or world historic, are potentially indefinite in number. The probability that the active cause is error or weakness is small.
Question: On what grounds does Brown, or anyone else, assume that these questions can be asked? In what conception of human activity are they grounded?
Note on the "a tendency to connect failure to error, defeat to weakness."
This was of course the premise of the Moscow Purge Trials.