Part of researching culture involves preparing to encounter words, ideas, and methods that change over time and that one may not agree with. More than that, one may encounter offensive and harmful words and ideas held up as authoritative, as truth. Know that not everything published in book form is true, and that every published idea is open to debate. You already have and are developing skills to confront problematic claims.
That said, please take care of yourself when you do research. Make sure you have the space and resources to process difficult encounters. Encountering claims -- made with great authority and backed by the scholarly community -- that directly contradict our own experiences and identities takes energy and resilience and it is wise to pace yourself and reach out for support when necessary.
The focus here is on the history of mathematical education, not the history of mathematical thought proper. However this text has an international focus that might help tease out some of the international issues in questions around “who does mathematics” and “who needs to learn mathematics.”