That open letter demonstrated a number of problems, not the least of which is the assumption that teachers are really surrogate parents of our children, whose job it is to teach our children moral values, namely their own. And the notion that taking issue with the slogan "Black Lives Matter" means that you think that black lives don't matter is also a problem. Most people I know who don't like that slogan think that all lives matter, including black lives, because we are all made in the image of God and are therefore of great and equal value. They don't like the slogan "Black Live Matter" because it presupposes that we don't already know and believe that black lives matter, and we find that insulting. It is itself a racist slogan aimed at white people who are assumed to be racists and therefore not to care about black lives simply because they are white.