Criticism: Someone writing a book quickly does not imply divine intervention.
Response: Read Did Joseph REALLY translate the Book of Mormon? for a clearer picture of just how remarkable an accomplishment the translation of the Book of Mormon is. There is a lot of research into this topic, all the way down to tracking down every shred of original Book of Mormon manuscript. The conclusions of that study are noted in the post. Compare all the research in the sources (there is much more out there) and it should be clear that Joseph Smith simply couldn't have accomplished the miracle of the Book of Mormon without Divine Help.