Complex sentence: The antonym "black witch" is an entirely modern creation as it was not previously needed; in the past witches were viewed, almost without exception, as malefic, serving as imaginary scapegoats on which diseases and bad luck could be blamed.
Split into simpler sentences: The antonym "black witch" is an entirely modern creation as it was not previously needed. Witches were, without exception, malefic and appear to have been imaginary scapegoats on which diseases and bad luck could be blamed.