It's quite clear that few of you have actually tried to teach English composition. I think Fish's approach is extreme, but it is quite valid. The arguments above about him not valuing content are, however, not. What he said wa that in his class what was important was syntactical structure. He probably felt that he didn't need to add that being able to construct a sentence correctly is a futile skill if you have nothing worthwhile to say.
I have taught remedial English to both children and adults. It is not an easy task. For most on this board, writing is almost as natural as breathing, but for a significant percentage of people it is not. They can "hear" a sentence in their heads. They can express it orally, in good form. They can even read someone else's prose in a logical fashion. But they simply cannot get it down on paper themselves in good English. I could give you examples (and I will if anyone is really interested). I believe that some people are "wired" to be able to write fluently and others are not. I have taught people who are very, very intelligent but who cannot, for the life of them, express their ideas in writing. At first I thought they were just being mentally lazy, but, given the desperation of some of my students and their willingness to spend time and effort to do something about it, I realised that I was wrong.
A knowledge of the general rules of grammar is absolutely essential to such people, because it gives them a framework within which to work while constructing written sentences. While they are learning those rules, the context or concepts are strictly secondary.
