Was it the case back in the day, though? I am not so sure about that. Of course there were plenty of people who thought this was a great injustice, but I don't think the general public back then would even raise a brow of condemnation towards a person claiming that this was ok and totally justified.
P.S. this is a total speculation about this specific scenario, but I had similar conversations about atrocities committed on the eastern front by soviet soldiers with my older family members who were young adults in 50s-60s in USSR. What I got was that their whole generation was pretty much on board with it, because, in their words, "Nazis deserved it" (with the implication being that every German person was a nazi, of course, even civilians). Not so much of a popular opinion these days.
These were debated as issues from the first moment. You had those who push for these kill all policies and those who oppose them. Sometimes one side win, other times the other and result is controversial from start for years.
There is this idea that "judging by the time" means judging by the perspective of worst person available, but that is not how history happened.