Ling Xiao's personality was indeed a much-needed comedic feature in their dangerous world. He had left the Diviner's temple because he felt that it was not the life he wanted, and after traveling alongside Xue Wei and the others for a long time, his true character had long since surfaced.
He had been taken to the temple at a very young age, and his entire childhood had been sheltered. He did not know much about the outside world, but his hunger for knowledge, and his curious nature made him escape the temple time and time again, with the purpose of learning about the real world.
It was not that Ling Xiao was ungrateful to the old men who had raised him, but he was smart from a young age, and he could sense the eccentricity in the way they tried to influence him. The constant belief that beasts were all evil and that the world needed them to subdue these beasts and make them work as slaves.