Interesting use of Plato's metaphor vis a vis scientology. I think Plato would have absolutely agreed with this:
Hubbard’s sought discard Truth and replace it with relativism
As to the 'cave analogy' -- I think Plato's meaning was a little different
Plato believed in absolute reality. Plato's 'theory of forms' describes two worlds (or realms of reality) -- the one we live in and a counterpart 'somewhere else'
What exists in 'the other world' are PERFECT examples of everything that exists in our world -- perfect trees, perfect brown rocks, perfect truth, perfect love, perfect musical notes, etc. etc. Everything that exists in our world are the imperfect manifestations of the 'perfect' 'forms' stored in some 'heavenly warehouse.'
The CAVE analogy:
Since MAN lives in the 'imperfect world' it is like living in a cave. The 'imperfect reality' man encounters is like shadows of the 'perfect forms (outside the cave) being cast upon the walls. What man experiences IS real (and true) but imperfect -- like shadows.
Man desires to know the 'perfect forms' but he can't access the 'dual world' directly. He can't get 'outside the cave.' The best man can hope for is to get a little closer to the entrance, a little closer to the light. A little closer to truth (through the practice of philosophy).
The 'cave analogy' is an indeed an allegory. Plato uses it as an illustration of Man's condition relative to the 'dual worlds'.
Plato's belief in a 'dual reality' is not allegory. He asserted that TWO worlds, actually exist -- one housing the 'perfect forms' and our world which contains only imperfect constructions of those templates.
As Plato's student, Aristotle saw problems with the 'theory of forms'. For example: leaves on a tree are infinitely varied in size, shape, color, etc. How does the 'perfect world' contain templates of leaves that do not yet exist? Does the perfect 'dual' world contain an infinite number of leaves? Or ONE 'ideal' leaf that is infinitely variable. These paradoxes lead Aristotle to reject the 'theory of forms'.
"What's True For You, Is True" ?
Plato and Aristotle would have considered this claim -- RIDICULOUS
Plato and Aristotle were actively opposed to the 'Sophists' -- the tutors of the day who taught logical 'sleight of hand' to the sons of affluent Greeks. Plato and Aristotle would have considered 'What's true for you...' mere sophistry.
Plato's diaologues are largely a refutation of Sophistry -- portraying Socrates confounding the 'sophists' in numerous debates.
Plato's 'theory of forms' is the OPPOSITE of "What's true for you..." since 'absolute truths' absolutely EXIST -- housed in the dual world. The close approximations of those truths mirrored in Man's world are also 'true' -- but they are imperfect. There's no 'relativism' in Plato -- these truths exist.
Aristotle believed truth could be ascertained in reasoned analysis, leading to what he called 'the Golden Mean'. For Aristotle, truth is found in examining a subject, dissecting it, tallying the score, finding points of consistency and finding points of agreement.
There's no 'relativism' in Aristotle, either. For Aristotle, 'What's true' is pretty much what 'reasonable men' can see to be obviously true, supported by common sense and analysis. Aristotle is considered the father of 'experimental method'.
Excuse me for going on quite so long.