Some apparently less common senses that Merriam Webster gave me:
- archaic : mild or pleasing in manner or disposition
- ready, fluent
- poised, assured
So what’s a “facile piece of writing”? Something that was easy to write? Maybe too easy to write? Or easy to read? (Or too easy to read…)
Well, something being easy is definitely an insult in the minds of pretentious people.
When used derogatorily it also carries an implication that something is 'pretending to be easy' while not actually being so. It might also tie in with Facsimile, but that might be a false etymology on my part. Which I guess ties this back to pretentiousness, but not quite in the way you meant to :).
Thinking ambiguity can be removed if you only use common words is misguided. You will get writing that is bland and lacks nuance and you may limit the palette of what you can convey, but even then without a fixed exhaustive definition for every word there is ambiguity in shades of meaning.
For example, what exactly does “common” mean above? “bland”? (writing is not a food, is it?) what precisely does it mean for writing to have “nuance”? and so on.
It depends on overall style, but I generally enjoy writing that thoughtfully sprinkles around less common or even invented (DFW) words. It keeps me on my toes—human memory is not perfect, if I haven’t had to consult the dictionary in a while then my vocabulary must be degrading.
Overall, based on all of the comments in this subthread, it seems that “facile” is most often meant simply mean “shallow”… don’t use a fancy word where a simple one will suffice.