1/3 of American Christians do think the bible should be taken literally, according to various polls. 56% think the bible should "have a greater role in society", yet - 57% didn't read the bible at all the year the poll was taken. 75% of people in the USA think the bible is the word of god, or inspired by god.
If you accept the Bible to be the "word of god", and most Americans do, then you are NOT taking it metaphorically. But, on the other hand most Americans haven't actually read the whole bible and only hear the "good" parts in church, as selected by their pastor. The evidence is overwhelming that most USA christians have a simple, literal, or almost literal, belief in the bible. They are not taking it metaphorically.
Once you decide that the bible should be taken "metaphorically" how does one decide what it really means? How does one decide which parts should be ignored? How does one decide which parts are good? It appears that most theologians are using rational, post enlightenment ideals, to cherry pick the good parts from the bible, and explaining away the parts that are evil, or contradicted by science as metaphor. Once you start down this path you are pretty close not needing the bible at all for your moral outlook, and discarding the iron age myths in favour of modern secular morals will seem a sensible step.