I think it's always preferable for educators to err on the side of caution when it comes to the language they use within the classroom.

For example, I see a major difference in an educator referring to "the crimes of White people" vs. "the crimes of White settlers/colonists." The latter is clearly placing the culpability on historical players for the systemic and humanitarian sins they committed. The former is implicitly extending that same culpability to all of the White students ("as a group") who happen to be sitting in that teacher's classroom. So I'm less concerned with whether the teacher points out that the majority of the historical offenders were White -- versus whether they are extrapolating from that fact to make an editorial indictment against all/most White people in the present day.

If you're a teacher who is directly referring to your White students as "oppressors," that's a problem -- to put it mildly.

As far as your kid's teacher who displays her "Black Lives Matter" banner -- I don't see anything inherently problematic with that. The BLM movement is intended to shine a spotlight on systemic racism that's pointedly directed against Black and Brown people, so that's factual. If that same teacher, on the other hand, goes on regular diatribes about "whiteness" (insinuating that her students are directly culpable), then it's time for the PTA and/or school principal to have a little private chat with her so that she doesn't create a social media shitstorm for herself (and for the school district).