The article, to my understanding, is not about whether Satan exists or not (despite the author's suggestion of the non-existence) but the role Satan plays in faith. On this count, I feel what he says is spot on.
Lucifer makes light out of what is dark and makes dark what is light. Love alone, not theology or Reason, distinguishes the differences, discerns soul from spirit. Listening to David unarmed, with nonjudgmental awareness, will help clear up the debate.