Hi Clive,
I'm afraid I won't say that I strongly disgree with your suggestion; I doubt that at the time I was writing my reply to Mr Pedantic I had your suggestion in mind. I believe I did read it, though, before I got to Mr Pedantic's, but I can't say for certain that it struck me as something I should address. Infact if you hadn't sent in this reply of yours I wouldn't have been aware of your suggestion. Perhaps what I had at the back of my mind when I was replying to Mr Pedantic's is the old standing debate in language teaching circles as to whether it is proper or pedagogical wise to correct students' errors as frequently as they come. I have encountered this debate among my fellow language teachers.
Now, my agreeing with Mr Pedantic's position, even if strongly, does not necessarily mean that I disagree with yours. I, myself, do not find it feasible to correct all errors all the time. Infact because I take a more functional linguistics approach to language, I do tolerate expressions which within the prescriptive mould would be marked down as wrong. Even my colleagues who are more puristic inclined do not find it, as you put it, practical to correct all mistakes all the time.
You wish to know whether I have ever taught a language class. Yes, I have! Still, I do make mistakes in my usage!
Hope this addresses the questions you raised!
Love!