Where are we going, Walt Whitman?
Walt Whitman's critics and fans for the most part agree that he writes without form. There's this idea, which he himself supports and encourages, that his poetry is naive, au naturel, barbaric and raw. In the main, everyone accepts this, and then they take sides over whether it's a good thing or not.
This makes sense, I think, if you think all form is restrictive and reactionary, that there is such a thing as complete rejection of form, and you accept this fight, or (not the fight itself, but) that the 19th century sides of this fight fully understand their own positions. It makes sense if you understand it in the context of 19th century Romanticism and Victorianism. If you accept that "form" means traditional, old fashioned, restrictive forms.
It makes no sense at all, though, when you realize Whitman was pioneering a new form, opening up forms, pushing poetry in new directions, liberating language for new forms and experiments and becoming a model -- a challenging model -- for an entire branch of American poetry, the branch that specifically wants to think about and thinks it's important to think about form.
Which is why William Carlos Williams, taking normal/vulgar speech like "I'll kick yuh eye" and "atta boy!" and showing how it scanned and had it's own metrical sense and was, in fact, more formally interesting than the flattened speech of traditional poetic forms, is so important, and also perhaps why his insight into Whitman is so unique and invaluable.