So for instance, the first chapters of Genesis and the book of Jonah are treated as parables or metaphors, not because there is any clue in the Bible itself that anything other than literal history was intended, but just because the critic can't accept what it actually says.
No, that's absurd.
The Adam & Eve story, the Noah story, the Jonah story all read as fables. If there were neon lights saying "fable" it wouldn't any clearer than it already is. If they were to read such stories in anything other than the Bible, people would have no difficulty in recognizing these as fables.
On a plain straightforward reading of the Bible, these stories would be accepted as fables, not as literal history.
The reason that some people take these stories as literal, is that they have been indoctrinated into the non-biblical theology of original sin, and they find it difficult to make a case for original sin if the stories are fables.