Difficulty for the writer means ease for the reader; ease for the writer means difficulty for the reader.This is why accusations that writing is unclear so often devolve into accusations of authorial laziness, and why defenses of dense writing so often hint that the aggrieved readers are lazy. This is why the discussion so easily becomes moralistic. (Work is after all a moral category.)
It isn't at all clear to me (modernist that I am) that it is easy to write dense prose, though. How does it change the discussion about clarity, if we bracket the above premise?