Plausible Deniability
One of the central ideas in Freenet is plausible deniability. All files stored on your Freenet node are encrypted (each with a separate key), and you have no way of knowing what they contain without access to the decryption keys which are contained in the addresses.
Of course, the decryption keys, which are contained in links to the files, may be publically posted on some other site - they have to be if the site creator wants people to visit their site. But if you've never had knowledge of that link, which is very plausible if there are thousands of Freenet sites, you can't be expected to know what is contained in the encrypted files in your Freenet node.
