I think the problem here is that politicians are mixing what happens in schools and what happens in the public. The public sphere has a bunch of people and interest groups very vocally airing all of the dirty laundry that they can find. And this will rightfully never change as long as we have a free society. I hope the vast majority of schools are more academic in class (especially K-12, there's room for more leeway in college as it's important to provoke and teach critical thinking).
Parents are mostly exposed to the hateful heretic-burning historical revisionism, not the careful, constructive, academic approach to telling the full story. When the kids come home saying that they learned X, Y, or Z about a historical figure, the parents assume (right or wrong) that they're being fed the hateful garbage that they see in the public sphere, so they lash out at the curriculum.
Some in the Left use that as evidence that conservative parents are hateful and (to quote OP) "don't want a society that is just", but what actually happened is that the parents were never given the opportunity to engage with the full story: they were taught the saintly version in school and then in later life exposed to the demonic version. As far as they can tell those are the only two choices they're being offered.
This is a good point I hadn't really thought about.
I think the lesson to pull from all of this is to try not to be a demagogue, and do your best to communicate in such a way that you can't be misinterpreted or misquoted as a demagogue.
