I can understand that some readers just see the words "concentration camp" and have a knee-jerk "eeeew!" reaction and downvote. They are frightened of certain topics without further thought. That's kinda forgivable.
But it's sinister that compassionate comments elicit a frenzy of flagging and downvoting. That seems worse than any simple "far right" sentiment. I'm starting to suspect there's a small but strong anti-humanist element around HN.
Edit: I'm quite sure there are vehement anti-humanists around here. The self-loathing is cloying.
You later clarified, but I suspect there's also a group of folks who don't want to hear that the US had concentration camps.
That's not sufficient for a good HN post, especially when the effect is to perpetuate a flamewar. The HN guidelines contain a point about this:
"Don't feed egregious comments by replying; flag them instead."
(which is our euphemism for please don't feed the trolls)