As an old fart who, when a child, was taught 'proper' by teachers who were certainly competent and often skilled I have seen many of the things noted above. Poor spelling, woeful grammar, inconsequential structure; yup, I've seen them all. When teaching biology to undergrads and marking their assignments I'd rip into all those faults and more and their response was usually along the lines of,
"The assignment was on biology. Mark that, not the English!"

For all the reasons given by previous posters I would sock it right back to them. And I often won them over.

But I suspect that blaming their inadequacies on "PC" might be incorrect; I don't see it as relevant in the parts of Oz where I've taught, although it may be relevant in some other cultures.

In a context where we're all exhorted to "Look at the big picture" I'd be more inclined to blame 'lack of attention to detail' for some of our students' inabilities. A recent thread got into a discussion of how to diagram sentences. I was intrigued and guessed it was about parsing; it turned out my guess was correct. I vaguely remember a few classes in junior high school that mentioned parsing and I even remember some of the terminology but I doubt I could do it. I certainly understood the structures of the various (supposedly tricky) examples used but I wouldn't be able to teach it, because I don't know the detail well enough.

For a better example from much basic biology lab work and we would teach how to set a microscope up so that it gave proper resolution; we'd also teach the difference between resolution and magnification and give them a competency test three weeks into the course. But it was only one of a dozen prac tests that they did and even many of those that set up their microscopes correctly forgot how to do it over the rest of that year. Some of those students of 12 years ago are now lecturing in that subject and requiring their students to sit the same competency tests.

Even if the lecturers 'cleaned up their act' and learned how to do it before teaching, they still approach the subject with the experience of "Don't worry too much about it", leaving unsaid the phrase "I got to be your teacher without worrying too much about it."

If insufficient attention to detail proves, by experience, to be acceptable in such technically-specific areas like biological microscopy (where at least the teachers can claim to be authoritative experts) what hope is there for schoolteachers of English, where they're in a minority of 'voices with authority', competing with TV and the students' parents and peers?

Cheers, Rowan