Of course, Long Yi was uninhibited, but Long Yi was no fool either. How could he simply let the chubby little guy leave so easily!
While Bangi was under Long Yi's control, Little Zi had exerted a powerful mental suggestion on Bangi. This mental suggestion would not exert much significant effect in the short term. But it would affect Bangi's entire growth process. It would make Bangi arrogant, unpredictable, selfish, full of lies, and disrespectful. In short, it would magnify all the negative traits of Bangi.
If from now on Bangi becomes a good child, these mental suggestions will not have any effect. If that were the case, Long Yi would not regret it, after all, he would have become a good child. But! Long Yi didn't believe he would become a good child! Since you've already gone bad, why shouldn't I make you even worse?