Why is it important that a historian considers people's perspective and biases; evidence; trustworthiness before they formulate their historical perspective?

It's important because they do not want to teach disinformation, misinformation, or just plain out lies. Here's an example, let's say a historian was asking a co.vid denier if co.vid is real, and if that historian didn't know any better then they will write that down and boom history.

Explanation:

This should be common sense not just for historians.

they believed democracy was worth the fight

the ss was the main organization responsible for the genocidal murder of around six million people of european ethnic minorities, essentially jews, in the holocaust. the members of all its branches committed war crimes and crimes against humanity during the second world war (1939-1945). likewise, the ss were involved in commercial enterprises and exploited the inmates of the concentration camps as slave laborers.

the tortures and assassinations committed by the ss were the result of an ideology developed long before the armed conflict, this ideology was based on the racial supremacy of the germans over the rest.