Oh, I fully agree with you that the "assigned interpretation" approach is stupid. Everyone brings their own experiences with them when they read a book. Everyone has different frames of reference.
The teachers' problem is that they're stuck between that reality and the curriculum, which says they have to teach _these_ moral lessons in English class, and do it with _these_ books. So they have to fit a pre-determined interpretation into the books, whether or not they even agree with it themselves.
I think my problem with that guy wasn't that he disagreed with the "assigned interpretation." He would say "that interpretation is WRONG," as though there is One True Interpretation, and He had found It. That's why he would argue with the teacher. If he would have just said "I disagree for _these_ reasons" then it would have been fine. But he wasted the entire class time trying to convince everyone he was right and she was wrong, which is just arrogant and stupid.
“As I am sure any cat owner will be able to tell you,
someone else putting you in a box is entirely different
from getting into a box yourself.” —bisexualbaker