As a teacher-in-training, I feel that I should say that while I do feel utterly appalled at Snape's pedagogical practices, there is a problem with reciting directly from the textbook.

That is, if you are quoting the textbook precisely, then how is the teacher to differentiate between remembrance and understanding? That is why teachers of more writing-oriented subjects often ask for the students to give their answer in their own words, to better gauge understanding.

There's also the possibility of the book having too limited a viewpoint, something that Severus "The Half-Blood Prince" Snape would definitely agree with, but he probably was just being a terrible human being, yes.