Harry scared the children because they were afraid of "cooties" which also made the girls getting away from him. However Mojo Jojo saw this and used Harry to scare the PPG to get away form the crime. At the end he kissed Blossom and then the girls all kissed him all over his face.
Although he was used for evil intentions, Harry himself didn't appear to be at all evil, rather just a boy looking for someone to return affection to him and not be afraid. Also, Harry didn't appear to be terrorizing off the Girls intently; he didn't even have to try nor did he have to say anything at all, be it menacing or reasoning. One could say that Harry was a living kryptonite to the Girls before they realized cooties were not real if he could defeat them so easily with unintentionally scaring them.
- His name is a pun of the term "hairy pits".