let me first argue the case that mankind is not inherently good.
We all would like to think that we are good. But, just because we think we’re good doesn’t mean we really are good. It’s like going into a calculus class and thinking we know everything. What reveals if you’re good in calculus is not what you think you know, but how well you do on the tests. Likewise, it is the tests of life that reveals our hearts.
Exhibit #1: Rhythm 0
Rhythm 0 (1974) was a six-hour work of performance art by Yugoslav artist Marina Abramović in Studio Morra, Naples.[1] The work involved Abramović standing still while the audience was invited to do to her whatever they wished, using one of 72 objects she had placed on a table. These included a rose, feather, perfume, honey, bread, grapes, wine, scissors, a scalpel, nails, a metal bar, and a gun loaded with one bullet.Her instructions were placed on the table:
Instructions.
There are 72 objects on the table that one can use on me as desired.
Performance.
I am the object.
During this period I take full responsibility.
Duration: 6 hours (8 pm – 2 am).
https://en.wikipedia.org/wiki/Rhythm_0
At the end of the 6 hour experiment, what do you think happened? A demonstration of the goodness of man? Hardly. In her words:
“What I learned was that … if you leave it up to the audience, they can kill you … I felt really violated: they cut up my clothes, stuck rose thorns in my stomach, one person aimed the gun at my head, and another took it away. It created an aggressive atmosphere. After exactly 6 hours, as planned, I stood up and started walking toward the audience. Everyone ran away, to escape an actual confrontation.”
https://debatingchristianity.com/forum/viewtopic.php?p=1002201#p1002201