Cliches versus Idioms

[busker]

The dreaded cliche . . . we should absolutely never use them. This is a hard and fast rule. 

But what about idiomatic expressions and vernacular language? Cliches are technically a subset of idioms. Is there a distinction to be drawn between idioms, vernacular language, and cliches? They can arguably be useful for cultural shorthand, establishing a time, place, or worldview. 

Where do we draw the line? Is it total annihilation of idiomatic expressions?

I don't think poetry is a tool for communication, because we don't live in pre-literate societies. Therefore, the need for a 'cultural shorthand' is questionable - exceptions aside. What hand are you trying to shorten here?

While you may write poetry for any number of reasons, the only reason that a stranger would read it is because he gets mental stimulation out of it. Now obviously, the more he knows about poetry, or the more adept he is at language, the higher the bar (note the idiom: but I'm not writing poetry). And here, readers of poetry, as opposed to writers, tend to be well versed, to borrow an idiom for the pun, in the craft of poetry. Just like, I suppose, hobbyist welders are familiar with the principles of welding.

To this market segment, idioms are lazy and sloppy. Why should I read her copy paste trite? They'd ask. 
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