While teacher unions do not directly create curriculum, the teachers are the ones implementing the teaching. When their focus is more on integrating social issues in the subject matter rather than actually teaching basic subject matter, it is a problem. When the leader of the largest teacher's union is focused on making up fake lists of banned books and stumping for bidens student loan pay back instead of worrying about how to fix the largest declines in math and reading scores in decades due in large part to her support and advocacy of shutting schools down(despite her complete lack of any medical training to form such opinions), I think that is a very good indication that their focus in NOT where it needs to be.
As to your question, my wife just finished her 31st year in public education as a special ed teacher, my mother was a teacher, and I know dozens of other teachers, administrators, school board members, the superintendent, assistant super intendent, and multiple district level administrators. How about you?
Finally, I don't know any child that has gone through k-12 that was taught segregation did not happen. I honestly don't think I have ever met anyone in my 50+ yrs on earth that doesn't know segregation did happen. How many people do you know that think segregation did not happen? Also, if we want to teach honest history, we should start by teaching that slavery was driven by $$$$ and not because white people hated black people. If you do not believe or agree with this please explain why africans were selling their own people as slaves? Were they racists or was it an economic decision? Slavery was/is a horrible, disgusting, practice that has NO justification or defense. However, it is not unique to America or to black people. I have no problem with teaching the truth about our history- particularly if it is in a history class.