Why are scientists nervous about plain speaking?

On the SciWri discussion board, several of my classmates have posted objections to our teacher's simplification and dejargonization of example texts.  One student did not approve of "cancer" replacing "malignant transformation." Another disliked "newborns" for "neonates."

All specialized training teaches new vocabulary, and part of the initiation into any profession includes adopting that new language, and if you don't, you won't be fully accepted into the tribe.  Problem is, you won't always be writing for people who share your private dialect. Even if they are also scientists, they might hail from a different specialty that calls things by different names, or even from exactly your own specialty but from a different era, before the latest, hippest lingo was current.

Or they might not be native speakers of English, and are struggling with the material, made worse by specialized jargon. (Unless they are Dutch and speak far better English than you do.)

You know how cops talk in court?  How they "exit the patrol vehicle" instead of getting out of the car? (See Val Van Brocklin's tell-all article "Cops Talk Funny," at http://www.officer.com/article/10249040/cops-talk-funny. ) The thing is, I'm certain that cops don't talk that stilted way in the locker room, to other cops. They "code-switch" to plain English when they want to tell the real truth.

Imagine if we could all code-switch to plain English and never switch back.