Something that stands out for me in your very interesting reports is that school subjects don't seem to mean the same thing as they did when I was the age of your children, and attending public school. 25-30 years ago, "science" was about things that could be observed, measured, calculated, and experimented upon. Label and describe the sub-cellular bodies. Calculate the workload using a single-pulley system, a double-pulley system, etc. What's the result when you combine chlorine and ammonia? (Evacuation of half the school, but that's another story.)
Your daughter's science class isn't about any of those things, but about political philosophy and other, at best, "soft" sciences. If there is any genuine science content, you have not yet mentioned it.
World history, when I studied it, contained facts about things that happened in the past in various parts of the world. We didn't have comparative religion presentations or attend fantasy films under the heading of "world history," although that might have been appropriate in a literature class.
I don't know whether this replacement of factual with opinion-based content is something that has happened generally with the passage of time, or whether it's a characteristic of your school/school system in particular, but I would find that trend to be just as disturbing as the ideological slant of the courses.
And regarding your son's letter, I agree with those who said that you've got an opportunity to show him how he could convey the same meaning in a more diplomatic way. What he wrote was not *exactly* rude, but it was very blunt, and some guidance would help him to be more effective in communicating in future.
Actually, it was rude. See my previous post on the matter. We're going to use this as an exercise in how to make your point and how NOT to make your point.