@Metallic blue light Gongja makes Kim Yul realize the irony. Kim Yul was bullied and wanted for his bullies to take responsibility. But along that path Kim Yul himself became even greater evil. Just like his bully "killed" him, he killed thousands people. And the worst is that he kept wiping his own memory. Every victim and death that was caused by his actions was forgotten by him. Now,just like he wished for his bully to take accountability, he wishes to accept the consequences himself.
Uncle is angry cuz it wasn't really uncle who took revenge, despite Gongja's promise. But Gongja laying out that path for uncle. Basically, he's mad that Gongja did all the work. And also got nearly consumed himself in the process. If not for the Goddess he might have never returned to real world. And that makes Uncle even angrier, hence he scolds Gongja about having too much compassion.
Uncle is angry cuz it wasn't really uncle who took revenge, despite Gongja's promise. But Gongja laying out that path for uncle. Basically, he's mad that Gongja did all the work. And also got nearly consumed himself in the process. If not for the Goddess he might have never returned to real world. And that makes Uncle even angrier, hence he scolds Gongja about having too much compassion.
