Firstly, it violates the family - friendly nature of Pokémon. This kind of fanfic can drive away many of the more family - oriented fans who have been with the franchise for years. Secondly, it can have a negative impact on the mental health of those who accidentally come across it, especially younger fans who may not be ready to handle such adult - like content. Additionally, it can also lead to legal issues if it goes against any trademarks or copyrights associated with Pokémon in terms of using the characters in inappropriate ways.
It can also lead to a negative reputation for the Pokémon fan community. People may start to view the fan base as being full of inappropriate and unethical content creators if such fanfics become widespread. Moreover, it can make the official Pokémon creators uncomfortable as it misuses their beloved characters in an improper way.
One negative impact is that it can corrupt the innocent image of Pokémon for young fans. Pokémon has a large following among children, and such inappropriate content can expose them to adult - themed ideas too early.