I’m writing an alternate-history story set in the 1630s and this topic touches on one of the plot points. My character is attempting to avert the various massacres of the 17th–20th centuries by engaging more strongly with the Christian community. I am receiving a great deal of resistance from Jewish readers who tell me that the character is violating halacha the way I’ve written the story, and that he would not realistically do what I am suggesting he might.
To what extent is it permitted to violate halacha to save lives? What are the limits on this, whether in the immediacy of the threat (my character is particularly trying to avert the Holocaust, four centuries in his future) or in what actions are permitted (for example, attending, but not participating in, non-Jewish religious services)?
Would any of this be affected by the appearance of a society (in this story-universe, a town of 21st-century Americans) that values religious freedom and is appalled by any form of religious pogrom or sanctioned massacre? (I.e., would the 17th century Jewish community be more likely to adapt their practices, or double down on status quo?)