The correct option is D Heresy
'Belief or opinion contrary to what is generally accepted' is Option D, Heresy. Option A, 'Unbelief' means absence of faith. Option B, 'Superstition' is a belief that is not based on scientific proofs but related to old ideas. Option C, 'Non conformity' is a deviation from a standard or an expectation. Thus, options A, B and C are incorrect and the correct word for the given phrase is Option D, 'Heresy'.