Despite being one who is not a fan of labels and categorizing, I still end up having the discussion in each of my high school poetry classes about what separates poetry from prose. We usually end up talking about three things:
the line, not the sentence or paragraph, as the unit of composition
heightened use of/attention to sound -- the musicality of poetry
If that doesn't describe haiku as well as mainstream poetry, I don't know what does.
Part of the problem, in my opinion, is that haiku is used extensively in elementary school as a way of teaching syllables. Because haiku is short, and because it's been taught to generations of children by teachers whose entire knowledge of the form is "nature and 5-7-5", many people -- including mainstream poetry editors -- have no idea that haiku is a rich and complex form of poetry. Haiku is seen as cutesy verse, and a book search at Amazon reveals that there is no shortage of published work supporting that notion, including "Pirate Haiku: Bilge-Sucking Poems of Booty, Grog, and Wenches for Scurvy Sea Dogs", "Redneck Haiku: Double Wide Edition", "Dog-ku: Very Clever Haikus Cleverly Written by Very Clever Dogs", "Robot Haiku: Poems for Humans to Read Until Their Robots Decide It's Kill Time" -- well, you get the picture.
I wonder what would happen if every haiku poet contacted five mainstream poetry journals and made the case for the inclusion of haiku. Maybe there hasn't been enough of a push by enough poets yet? I don't know.
Mr. Kacian, thank you for establishing this forum. What a great resource.
P.S., Hey, Don, you and I were typing at the same time, but you finished first -- I agree with what you say and I hope you're right that haiku is going to be "nudging other poetry genres a bit to the side".