e., speak up against Hitler's treatment of the Jews, but at great risk to themselves. To be a member back then of one of the various resistance movements against Nazism throughout Europe was to clearly practice moral virtue and to speak up against a group hurting another group. But it took enormous courage (emotional courage and the courage of one's convictions). Further, if one were to be caught by the Nazis being a resistance fighter, one would be taken prisoner and hanged. Those who practiced moral and ethical virtues to the greatest extent during the Holocaust, though, did speak out, even at their own potential peril, since this was the moral and ethical thing to do although obviously not the easy thing. But the majority of non-Jewish Europeans did not try to interfere with the Nazis hurting the Jews nearly as much as should have been done. This was for the same reason people often do not...

In this case, European people had to choose if they would act according to human virtue, ethics, and moral standards and speak out against the Nazis, or if they would instead say nothing and in that way stay out of danger themselves.
In choosing not to protest, those who made that choice instead of speaking out against such mindless and irrational persecution of Jews on the part of the Nazis, where not doing their human duty to behave morally and ethically by stepping in, or at least trying to, in order to try to stop the persecution of members of one ethnic group. That was those peoples' moral and ethical duty as human beings, but most European non-Jews lived through the Holocaust but did not practice moral ethics as much as they should and could have done.