well, it is a big deal if we can persuade them to slaughter whole peoples (Jews, Slavs, Gypsies). It makes us worse than animals...
Also, what is horrifying about the holocaust is that many if not most of the Jews of Germany were heavily assimilated. They looked no different, dressed no different, spoke no different than any other German. Hitler in the MK points out about Hassids in Vienna, which was a multi-cultural center, but in Germany proper there were few such distinct Judaic peoples.
To whip up hatred against an "other" who looks, acts and talks the same as you or me speaks poorly for the human race.