In short, the purpose of this course is to help you learn what distinguishes great writing from so-so writing from outright bad writing. One of the first things you should acknowledge if you want to learn how to be a good writer is that good writing isn't boring. You don't have to agree with its message or be convinced by its argument, but good writing is thought-provoking, interesting and above all, something worth reading.
Whys is it these things and not, say, unoriginal, bland and not worth reading? Because every piece of good writing, in essence, is a conversation between the reader and the writer. Inherent to the idea of writing as a conversation is notion that the author is trying to instruct or argue something to the reader and the reader is either being persuaded or being stimulated to think about contradictions to the author's point of view. Although the reader very likely will not have the opportunity to directly interact with the author to bring up points he/she agreed or disagreed with, the act of "conversing" with an author as a reader is a way in which a piece of writing leaves an impact. Of course, conversations can be one sided, but generally speaking, they aren't very interesting if one side monopolizes the exchange. If an author allows for no room for counter-argument or merely presents a laundry list of facts and statistics, there's no much room for a conversation and thus, not all that much value of intellectual stimulation to the reader. Good writing should not just inform, but it should spark interest in the reader to read, research or even write more on the topic.