What is meant by "rhetorical competence"?
In addition to writing with good grammar and usage, presenting good arguments (without fallacies), acknowledging (and blowing away!) opposition arguments, etc., in writing or speaking, people also need to choose their words carefully so that their meaning is crystal clear without strange references or anything else that would cloud their thoughts.
Here are some articles on the topic:
http://www.google.com/search?q=%22rhetorical+competence%22&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:en-US:official&client=firefox-a
And one blog post in particular from 2003:
http://www.slate.com/id/2092608/
Read all the way through; the use of the phrase "rhetorical competence" is used just before the Update.