Who according to King will not like the idea that competent writers can be made into good writers?

Stephen King stated, in his book On Writing, that "...while it is impossible to make a competent writer out of a bad writer, and while it is equally impossible to make a great writer out of a good one, it is possible, with lots of hard work, dedication, and timely help, to make a good writer out of a merely competent one."

He went on to say that this idea is rejected by lots of critics and many writing teachers. Basically, he said that they can be stuck in the mud and very rigid when it comes to ideas about writing and people's ability to write well. So, the answer to your question is "lots of critics and plenty of writing teachers."