I don't actually believe all people are universally "good and kind" they/we are "good and kind" to those "like us" and who we think are deserving.
We're seeing that issue in our own country right now. We are seeing it on these very boards.
Just look at the discussions around immigration, brexit, benefits, disability, mental illness... People are more than happy to vilify and discriminate against people who "aren't like me"
Hitler etc understood/understand that and capitalised/capitalise on it.
The oft cited poem by Martin niemöller perfectly encapsulates that.
Also when resources are or appear to be finite/restricted people become afraid that they and theirs will suffer as a result of shortages/lack of access to essential resources. That is pretty much the main cause behind most wars - the gaining of wealth/resources.
I've lived in Germany, for the most part the Germans I met were ashamed of this part of their history - but not all of them by any means.
I met older Germans (old enough they were teens/young adults at the time of WWII or not much younger) who were unremorseful and still arguing (this was in the early 90's) that what was done was necessary to create a better functioning, wealthier Germany, who were still saying things like the Jews were hoarding wealth, were lazy etc I also watched some documentaries while I was there (shown on German television) interviewing people who'd reported Jewish neighbours in hiding etc who again, had no remorse and still firmly believed they did the right thing.
These were not particularly unusual people, these were ordinary people either working ordinary jobs or housewives/mothers.
The closest thing to remorse on he most shocking documentary I saw was a lady saying "that's just how it was. That was the law then who was I to question the law?" That's really stuck with me.