Well this stuff is "divisive" because it's become a culture war. However, what some of these teachers want to teach is also "divisive".
Point being, we don't indoctrinate children with whatever the latest fashion happens to be in left-leaning circles. Rather, we insist that, in general, (allowing some exceptions), teachers have to be politically neutral and not try to push particular perspectives on their audience.
Some teachers have been acting in ways that are not only unethical, but against their legal duty. Of course they aren't going to like being told to "stop doing it", of course they are going to find that "divisive", or pretend it's "divisive" anyway. They are throwing out rhetoric because they want to keep doing their thing.