Of course it backfires somewhat, because if the oppressors can have disdain for the language of the poor, it's one more dehumanization. But it also provides pride and exclusion for the dispossessed.
Note: by "exclusion" I mean the closing of an in-group against all others; this is a necessary survival mechanism for the repressed and dispossessed.
Of course exclusion is also used by oppressors to solidify control in the hands of THEIR group, so it's a double-edged strategy.
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