From both a practical and human-rights perspective, it is wrong to teach history supporting any one political stance

Practically speaking, this kind of propaganda alienates a large portion of the voter base, opens the door to valid criticisms from the opposition, and drives reactionary trends towards White nationalism. Ethically speaking, since K-12 education performance is used to determine college admission and thereby job prospects, the political positions of children (which are not necessarily the same positions they will hold as adults) would impact their future. I don't care how adamantly you say that teachers should grade from a neutral perspective so long as a child's argument is well defended, this is completely unrealistic. All humans are both consciously and subconsciously biased and these courses only allow that bias to impact the futures of children. It also opens the door for extremist professors to grade with a racist and sexist bias against White men. For example, I have had a professor of intersectional feminism in college dock me points simply for being a White man. I know this because I completed the reading and provided an analysis (which did not contradict but even expanded upon the opinions of the professor) in much better English than 90% of my classmates (and the professor herself), yet was docked points for a nonsense reason. She said I hadn't provided "analysis" of the document even though I clearly had. I was forced to drop the class, losing money and wasting time, based on the racist and sexist actions of a professor who claims to be against racism and sexism. This sort of abuse would only go on further in a classroom with young, impressionable children. I strongly believe that the rise in White nationalism and racism in America is a reaction to the rise in alienation and mistreatment that White people face from the left.
Current history courses in K-12 sufficiently cover the topic of slavery and racism in the United States. Obviously, efforts from the right to eliminate these from the curriculum need to be resisted. However, the left's hyperfocus and hypersensitivity around race these days has been extremely harmful to race relations and the efforts of true liberals, egalitarians, and socialists. Racializing issues that we all face by viewing them through a theoretical lens muddies the waters and opens up opposition from White straight people who could be powerful allies in the struggle for equal and plentiful human rights. Nobody wants to be made to feel othered. That has been the impact of excluding Whites, straights, or men as a class from the issues of those belonging to varying intersections of minority groups. That isn't to deny that there have been and are White, straight men who have done wrong by other groups (certainly, this topic is covered extensively in modern education at all levels as it should be). However, the current modus operandi of the left regarding identity politics is reducing the power of the Democratic party to affect change through populism. That's why Trump won in 2016. Frankly, we on the left need to stop trying to push the Overton window with fringe sociological theories authored exclusively by and for lesbian Black women. Their voices are just as important as those of any other American, not more so. Highlighting issues which could by faced by anyone as specific minority issues is not popular or effective at producing real change. Instead, issues should be tackled from the perspective of practically affecting the most positive change for the most people, without ignoring the issues of minorities. When equal rights for all is the basis for change rather than a specific focus on advancing the outcomes for certain minority groups, I think we will find that the Democratic party gains more popularity and thereby more ability to write policies which inevitably benefit those very same minority groups.
Yes, there are both historical and contemporary issues of racism that need to be discussed in an educational setting. No, they should not be given any more importance than any other issue, nor should any one group be touted as more or less oppressed than any other. This is counterproductive to examining specific instances of inequity, since racial theories tint the lens through which we view facts.