[Rhyme is] no necessary adjunct or true ornament of poem or good verse, in longer works especially, but the invention of a barbarous age, to set off wretched matter and lame metre; graced indeed since by the use of some famous modern poets, carried away by custom, but much to their own vexation, hindrance, and constraint to express many things otherwise, and for the most part worse, than else they would have expressed them.

- John Milton (1608-1674)

Not necessarily true, and certainly questionable, but it I find it beautifully formulated and highly interesting.