@croydon - I don't really believe that. Poetry should be free to be written in whatever style it needs to be written in. I don't really see emulating, say, the Robert Frost style of poetry as any different from "copying" the sonnet form of poetry. It's only following a set of rules in order to put restrictions on a piece.
Working within those restrictions can be a real pleasure and it can strengthen the work. Even Marianne Moore, whose poems look as though they are free form, almost always picked a particular form, like a certain number of syllables per line, and stuck to it.
Not only can this improve the rhythm of your work, it forces you to consider every word with care. And to some extent, I believe that's the point of poetry. To create something beautiful and intricate from words, where every word counts towards the end.
If those words are chosen according to certain rules I don't think it changes the substance of the poem.