He was very calm, not mad, not deranged, just like he was talking about what he had for lunch, saying: "Can we destroy this world? Like with that Star Annihilator Cannon, just wipe it out, there's really nothing to hesitate over."
"Do you really not want to save your own people?" Xue Dili retorted.
He had seen Faust's memories, and Faust had truly wanted to save his people before. He wanted to abolish the courtesan system, and then he wanted to abolish the gang system, until he discovered that the backers behind the gangs were the Mysterious Nobles, and he directly talked to the Twelfth Apostle about eliminating the Mysterious Nobles.
But no matter what, all he got was one sentence.
"Sir, this is too extreme."
So in the end, Faust only wanted to burn this entire world to ashes. He couldn't save it, so the only option left was to destroy it.
An equal and painless death is better than living in despair in this world.
