But copy editors shouldn't have to justify their jobs.
Copy editors are who save your article from being in the anals of history.
We're the ones who advise against doing great pubic services, getting caught in a vice grip, or seaming week.
We also check your math (does that new treatment increase survival rates by 16% or 16 percentage points?); review sources to confirm that hot tip wasn't a from Russian bot; check whether Colin Farrell's iconic scene in 'Pride and Prejudice' was in fact Colin Firth's; remind you Ivana was the wife and Ivanka's the daughter and that Charles Lindbergh was the antisemite superstar pilot while Howard Hughes was the jar-peeing superstar pilot; and fix wacky spelling and punctuation errors--which reminds me, do the semiautomatics used by "eighteen year-old Marines" have a specialized grip for toddler-sized hands?
In short, it's a terrible idea to fire your copy editors. When the Post tried it, errors exploded. Trust in the paper dropped. (See, e.g., here.)
So be nice to your copy editors. There they're to save your assess.