Not my criticism, Thatbags I have said nothing against the author of that letter except that I myself would have not have written it quite like that. Some people, granted, were more critical.
It is true, however, that some teachers do not have a very good grasp of English grammar and spelling - probably because when they were at school the emphasis was on the content rather than on the "rules". The pendulum had swung a bit far. I was arguing that they really should be au fait with what they are employed to teach. Diversions into the time when teachers could not be married were irrelevant. I was sidelined into inaccuracy, which was fully exploited by our resident unloving man.
As Penstemmon says, a struggle with a subject makes you more careful to put it over so that is understood, that does not mean that no-one can comment on a mistake made by a teacher. In their own field, yes, they should take care not to set a bad example, which is likely to be the one thing more copied than all the good ones.
I may have exaggerated a bit about your different points of view to teachers, but where you you were right, I do sure that they accepted your opinion.