I think you were misreading the dialogue between Lurker and Ja Wangnan.
Lurker was basically saying everyone in the Tower are hypocrites. There aren’t any good guys and Lurker isn’t trying to be one.
Ja Wangnan forgiving Lurker was basically him saying “You know what? You’re right. How can I be mad at you for pulling the same kind of shit as I will if that’s what it takes to climb the Tower?”
This wasn’t a moment of Ja Wangnan deciding to follow a better path but rather of him acknowledging his own hypocrisy.