This article suggests the question when writing a poem: what is the constraint? What is the constraint against which the expression builds and/or relieves tension? If not rhyme, then it could be alliteration, consonance, assonance, meter, cadence, syllabics, chiasmus, or repetition (e.g. tritina, pantoum, etc.) What makes it something other than hyper-lineated flat expression? I read somewhere recently the claim that the problem with "no ideas but in things" is that people will list a bunch of things and call it a poem. It's left up to the reader to find the poetry in it. That may or may not be a legitimate claim. These bigger questions sometimes bug me, especially when I uncharacteristically find I can't sleep at 1 am.