If sources for some practice are one-sided and especially talk about negative things, usually you can discredit those sources. Let me give you one example. Teutonic Knights liked to blame Pagan Lithuanians for sacrificing people. But the reality was pretty different. The Grand Duchy of Lithuania was a Pagan state that was invaded on the basis of a "holy" crusade declared against this country. And Teutonic Knights were the main executors of this crusade. In practice, those knights did the following. Murdered people, burned Lithuanian lands, raped women and children. And Lithuanians, since they were not intoxicated by abrahamic religions, fought back as best as they could. And in some cases, they caught some of the knights. They were not sacrificed on religious basis as Pagans saw them unworthy of such death. This means that no Lithuanian Pagan priest participated in the burning of some criminal knight. Those knights were executed by burning them alive on orders of military leaders, dukes, etc. Like war criminals, rapists as they were. Those knights that were adequate and humane were not killed in such a way and even grand dukes like Kęstutis spared most of them. However, the Teutonic Order always wrote in their sources that Lithuanians were some human sacrificing murderers. Of course they won’t mention in their sources of their own crimes against Lithuanian people.
If you really want objective historical truth, you must look into different sources. Ideally, the origins of those sources must oppose each other ideologically, culturally, politically, etc. Meaning basically the following. If sworn enemies write about something the same thing, then it means this thing should have been true. E.g., if England's and France's sources claim that some pope was a pedophile when those two countries waged their own hundred years war against each other, we can definitely assume that this pope indeed was a pedophile.