To conflate fantasy with immaturity is a rather sizeable error.
Rational yet non-intellectual, moral yet inexplicit, symbolic not
allegorical, fantasy is not primitive but primary. Many of its great
texts are poetry, and its prose often approaches poetry in density of
implication and imagery. The fantastic, the marvellous, the impossible
rode the mainstream of literature from the epics and romances of the
Middle Ages through Ariosto and Tasso and their imitators, to Rabelais
and Spenser and beyond. This is not to say that everybody approved of
it. Conflict with religion and with realism always loomed. In the first
great European novel, imagination and realism meet head-on, and their
contest is the very stuff and argument of the book. Don Quixote is
driven mad by chivalric fantasies - but what is he without his madness?
Shakespeare may have influenced English literature towards fantasy in a
rather particular way. Spenser has Continental counterparts, but A Midsummer Night's Dream and The Tempest
do not. Nowhere else in Europe did folk tale, legend, medieval romance,
travellers' tales and individual genius coalesce in such works of
imagination as those plays. That may be one reason why the literature I
am talking about is very largely an English-language phenomenon.