That Freenet is currently filled with it is a good thing -- it indicates how much pressure society puts on the people who are into this stuff and that no other group, such as the KKK, gun rights activists, astronomers, has that much reason to fear going public with what they right.
And any such group will quickly fill freenet up with other content, as it will be much bigger than the child abuse rings.
And while 16 year old sexting would be considered cp I highly doubt they would be uploading it to any such networ, if only because they don't want others to see them.
Is that true? How would you know? Is there statistical information out there about what fraction of the population is aroused by child pornography? Given your statement about naked 16-year-olds sexting falling into that category, it seems implausible.