Asklemmy

From what I understand, modern historians are much better about this. You'll see this in the approach of historians from a majority culture who are combing back through established narratives and dismantling misleading ones. But historians in the past have absolutely taken liberties to trash people or civilizations they personally disapproved of, never mind thinking through their personal biases.

If you ask this on the basis of high school textbooks being used today, I would mention that they lag far behind the practices of modern historians. Although teachers in these settings will often use primary and secondary sources to illustrate the pitfalls of relying solely on the latter and other further removed materials.

Like with the journalist question, many people take on the title without the qualifications or ethics, merely using it to promote their slant, which I will grant often makes for a more exciting story.