If you can get exact collisions, this can be gamed. For example, suppose there are two rival gangsters. One wants to set the police on his rival. He knows that a certain (innocuous) image is on his rival's phone. So he pays someone to generate a fake child-porn image with the same neuralhash, and ensure that it gets into the child porn DB. Then, apple reports the rival to the police, and they come and investigate him. OF course, they may notice that the image isn't the right one, but by that time they may have found other incriminating evidence.

Not sympathetic to a rival gangster? Ok lets find an innocent victim: not a rival criminal, but an innocent witness who our protag wants to intimidate. Gangster wants to intimidate the witness, but can't get at them, so cooks up a scheme to convince the witness that the police are in his pocket. Exactly as above, causing the police to investigate the witnesses phone.

Another one might be, a certain government wants to identify opposition groups using images associated with them . Apple is not keen to be associated with that, but the government can simply generate fake child-porn (remember, programmatically generated CP is just as illegal) for each image of interest.