It strikes me that there's a difference between pessimism--which I view as a species of realism--and 'defeatism.'
To me--someone who is eternally and prob'ly irredeemably pessimistic--it is NOT 'defeatist' to assume the worst (or if not 'the worst', at least the bad), and to work to mitigate it, even without hope of success.
To look into the abyss, to recognize it, and continue anyway in the face of apparent futility, in the full knowledge that you will likely NOT prevail against conditions which confront you, seems to me the only way to live authentically...
Perhaps it is self-serving of me, but that strikes me as 'courageous,' rather than 'defeatist.'
20 hours ago