Yes, you avoid idioms in writing if you want it to be clear. If you're going for style, as in fiction writing or for artistic purposes, then do whatever you want.

I'd like to see an example of a good writer, or even one sufficiently long piece of clear writing, that doesn't use idioms. Language is saturated with them.

You'd be on more solid ground (and closer to your point about loops) to say that, when teaching foreign languages to beginners, idioms are best avoided because the student is struggling just to know the individual words. Even then, though, I doubt I ever took an introductory language class that didn't teach at least some idioms; you can't get a feel for a language (or fully understand any real-world text) without them.

>I don't know where on earth he got "By definition an idiom is something you remove from good clean writing," which is obviously not true

Maybe from all those classic books on writing, like the "Chicago Manual of Style", "On Writing Well" and "The Elements of Style", which all agree on the point.

Where you got this bizarro impression that idioms are NOT to be avoided in writing? Idioms are cliches, and they needlessly obfuscate a text.

I suppose it's foolish to belabor the point, but (a) is it just me or are you sounding a bit of a bully? and (b) everything you wrote is untrue.

My impression comes from observing language: it is saturated with idioms. You can't throw them all out (without a lot of unnatural effort) nor is there any need to. You might as well say that a musician should use only notes and not chords, or avoid standard chord progressions. If you can find any significant piece of writing that avoids idioms, I'd like to see it.

Idioms are not cliches. An idiom is a phrase whose meaning is more than the sum of its words. A cliche is a phrase that has become hackneyed through overuse. (Nor, by the way, are cliches necessarily obfuscatory. "Get your ducks in a row" is, but "Live and learn" is not.)

Style manuals have their place but are hardly scripture, and there are countless examples of great writers breaking every rule in the book. Indeed, Strunk & White breaks its own rules, sometimes when describing the very rule it's breaking (which is part of its charm [1]). So even if your claim were correct, it wouldn't prove anything. But I'm pretty sure it isn't correct. Since you claim that Chicago, Zinsser, and Strunk & White all agree on the point, please show us where; I'd like to see. All three of those texts are searchable online and I couldn't come up with anything. But I only tried for a few minutes.

[1] Just for fun, here is an example: "Students of the language will argue that try and has won through and become idiom. Indeed it has, and it is relaxed and acceptable. But try to is precise, and when you are writing formal prose, try and write try to." How can anyone not love E.B. White?

This is probably completely apparent to anyone who's had to learn an ancient language (4 years Jesuit high school Latin can I get a qui qui?!) --- to understand ancient Latin you need to learn the idiom, not because the Romans were overly fond of cliche, but because they were speaking in a different historical context in which their audience could be expected to understand that "nut" was synonymous with "toy", or Greeks could be expected not to track dates on calendars.

So just as reading the simply Yacc grammar for MRI Ruby is not a particularly great plan for mastering Ruby, learning the rules of grammar and memorizing individual vocabulary words isn't going to give you convincing conversational mastery of a spoken language.

>Style manuals have their place but are hardly scripture, and there are countless examples of great writers breaking every rule in the book. Indeed, Strunk & White breaks its own rules, sometimes when describing the very rule it's breaking (which is part of its charm [1]). So even if your claim were correct, it wouldn't prove anything.

Breaking a rule ocassionally is not the same as not having the rule on the first place. For one, they can "break their own rule" precisely because the rule exists. They break the rules they set with caution and only when the feel it is needed. That's the way it is with most rules, about writing or anything else. The rule provide a guideline for the 90% of times.

(Edited to be less irritable.) You haven't replied to the main point, which is to give examples of your alleged rule from the three style guides you cited. As far as I can tell, it's not in any of them.