Hard to believe what some people can do to others.
I know what you mean, but sadly, for me, it’s not hard to believe.
Nothing matches the holocaust in scope, as well as the genocidal intent (in essence the attempt to eliminate an entire group, millions and millions, of people) and sheer volume of murders. It was literally industrialized state sponsored murder of millions.
Yet there are numerous other examples of other genocidal systematic mass murders in the 20th century alone, albeit not reaching the scope of the holocaust.
The Turks campaign against the Armenians at the turn of the century, the systematic brutality and murder of millions of Chinese (and other Asian races, estimates of millions murdered) by Japanese invaders during WWII, Stalin’s post war murder of millions, Pol Pots mass murder of millions of Cambodians in the 70’s, and later the mass murder of close to a million Tutsis by the Hutus in Rwanda.
I’m sure I’ve missed a few in the last century. That’s just in the 20th century.
So, yea, Homo Sapiens are a fairly bloodthirsty species.