oda says his editor makes it that way so it looks cool
This was real life. Shanks was no longer just a character. He was a person. A normal human. Even a 'good' man can commit atrocities in the name of his own justice.
In ancient times, it was power. In the modern world, it was money. In this future where human lives were as insignificant as grass, it was... Strength.
Apocalypse: Infinite Evolution Starts from Attribute Allocation