The requirements for home schooling in the US vary wildly from one state to the other and can be almost devoid of any practical oversight in some circumstances. In most cases, parents have autonomy to choose their curriculum and there is a whole industry built to cater to that market. Unfortunately that includes books that deliver the kind of stupidity that we see above. Also, I think it is difficult for those outside the US to understand just how much we idolize individualism over any sense social responsibility here.

I’ve observed several possible explanations:

1. People are taught certain doctrines and will not question those doctrines - ever. If some new information conflicts with those doctrines, then their faith is being attacked.
2. Some are deeply invested in what a certain doctrine allows or prohibits. Think about the sick rationalizations for slavery in the US back in the 1800s supposedly based on the teachings of the Bible. (Sorry, slavery fails the “love your neighbor as yourself” test). To change their thinking means that they have to admit that they were wrong or give up some privilege or perceived position of superiority.
3. They self identify with those beliefs and anything that contradicts that belief is a personal attack. Basic arrogance.

From my perspective, the teachings of Christ were about humility. Admitting that you were/could be/are wrong and being willing to change. That’s the whole core of acknowledging your own selfishness (sin), moving to repentance (change) and seeking God’s help in that process. Being combative is not compatible with that, in my views.

I was thinking about how to reply here in a meaningful way but I think your response encapsulates the core of it pretty well. Lots more I could say, but would lead to long essay and probably of limited interest to the topic at hand.

We homeschooled our kids for non-religious reasons. Most of the commercially available books, materials and curriculums were Christian oriented. While I am a Christian (although not a conservative) I found some of the materials just flat out intellectually insulting, factually incorrect, extremely biased (without the benefit of scriptural justification) and the above example is far from the worst of what I saw. It says a LOT about where your faith actually lies if you have to promote a false reality to justify it.