Harmful to society? And exactly how does that jive with the fact that individuals have rights and not society? That you can't harm society you can only infringe on the rights of an individual... as only individuals can have rights?
Having child porn does not harm anyone. Especially when it's completely fictional. The person who committed the act with the child MAY have. The government definition of child is way out of line. A post pubescent individual is not a child.
A real crime, a natural crime has a victim. A real individual who has had their property rights infringed. Having images of a crime is not a crime. There is no victim. It's nothing more then a thought crime and totally illegitimate in a so called free country.