One; that was only revealed after the fact, specifically after his redemption arc started, and it probably was only done as a sort of retcon to downplay what a monster he was initiallly introduced as, probably due to how popular he became.
Two, it still doesn't change the fact that he did just that, and then the series expected the readers to forget about it.
Don't misunderstand me complaining about this as me hating on him. I am pointing out that MB was trash and the author wasn't really being meta or anything like that. He was pulling shit out of his ass to lengthen the series, same as any other mangaka to ever work on shounen.