If Einstein then asked them to be quiet so that he could teach, 10 of them would collaborate to write a statement that he said something sexual or threatened them, and then Einstein would be removed and put into the Absent Teacher Reserve or worse. Whatever the kids say is "substantiated" and the teacher is not believed at all. The teacher's authority is undermined, heck, blown to complete hell. The teacher is the prey of the students, who don't want to do any work and yet want a passing grade.
But all you can complain about is teachers unions. Walk a mile in the moccasins of a NYC high school teacher, then get back to me. If you live long enough. I've seen 2 colleagues carried out on stretchers and numerous others assaulted and injured.
These are problems as well, but don’t try to tell me the unions aren’t protecting bad teachers — or that knowledge of subject matter isn’t a fundamental problem because as a teacher I know better than that. I’ve seen too much get a pass here in the deep south. (And please re-read my post because unions were not “all” of the problem — and I did not say they were!) Try reading with a little less defensiveness and a little more objectivity.