Kent's take on the effect of WCW/Rakosi-style prosody (in his essay linked here yesterday)  is the opposite of Mike's & New Formalist theory.  Kent says that the unpredictability of same creates the possibility of clearer poetic perception, less mediated by ego or tradition.   NF theory, as Mike has described it, holds that the metrical patterns & their variations help create the conditions for meaning to emerge.
 
These are basic 20th-cent. positions on the difference between free verse & metrical form.  Pound sought to "break the pentameter", pushed for ideograms/imagism.  Stevens, I think, used rhythm - with both free & metrical bases - as one facet of his own musicality (which also employs phonic values, repetition, fantastic vocabulary, and other means toward this end).
 
The idea that poetry fulfills its function by reflecting natural & divine order by means of measure & harmony is very olde.  It hasn't gone away, either - witness the various theories promoting iambic pentameter as based on biology and natural form  (cf. - for fun - Sir Thomas Browne's Garden of Cyrus for the prevalence of the number "5" in nature). 
 
The general critical take on Modernism, though - reflected in Kent's analysis of Stevens - has been that this intellectual/artistic era had no faith in overarching order or natural harmony : rather, art imposed its autonomous orders as a guard or protest against the violence & chaos "outside".
 
So the free-verse/postmodern/(Taoist, Kent?) position faults metrical formalism on two counts: its idealism and its traditionalism. The idealism layers over nature with an imposed order; the traditionalism blocks innovation & new perception.
 
How to get beyond these (rather worn-out) dichotomies?
 
Rather than arguing that "there is no such thing as free verse", say : all verse is free.
 
How so?  Verse is free in the sense that the poetic word can function as both music and anti-music, as order and disruption.  Poetry can be song, but it is not only or necessarily song.  Poetry can be the closest thing to a curse, or to silence itself.
 
I would say that the activity of the poet is essentially an orientation toward harmony.  But harmony operates on more than one level : there is an intellectual as well as a sensible harmony, and sometimes the former counters, opposes, negates the latter; sometimes sensible harmony is configured ironically to veil a very different intellectual substance.  Intellectual harmony is logical, reasonable, ethical : it may have formal or mathematical or aesthetic aspects - but these elements may be at work to break superficial or oppressive "harmonies" of "nature".  It may be subversive in this sense.
 
Order, pattern, harmony - the interwoven wheels and forms and numbers of time & nature are irreducible facts.  We take physical pleasure - perhaps even physical health - in the octave and the circle of fifths and the pythagorean triangle & the shapes and colors of leaves & sky & fresh air.  But when Stevens, say, writes that "poetry is the sanction of life," I don't think he's granting poetry such prestige simply because of its ability to mimic or model the physical harmonies of nature.  The freedom of the poet to find and articulate intellectual harmony - another name for it might be justice - functions at the active, living center of the purely aesthetic or natural harmonies.
 
So these general notions of the poet's role have some implications for prosody, perhaps.  The sovereign freedom of the poetic word moves toward musical harmony or against it, at will.
 
The general ground I'm trying to sketch out here, though, doesn't support the arguments of the free verse wing any more than it does the New Formalist.  I repeat my comment posted yesterday:  the argument that WCW/Rakosi style imagism or impressionism allows nature or reality access to the poem, in a way that a more rhythmically-patterned prosody (such as some of Stevens') does not, avoids the whole issue of pattern and regularity and form in nature.  The coherences of formal repetition in poetry can represent the fantastically interwoven coherences of natural ecology:  the subsuming of line to stanza to poem can mirror the overlay of forces and powers which move through time and space, and also the overlay of themes and meanings which the poet wants to emphasize or interlace.  These patterns have at least as much reality as the contingent perceptions of the romantic imagist.