Also, it seems that your parsing process strips headers and that you don't keep the raw messages, however I remember that on some newsgroups people used to pass secret messages in headers that only those "in the know" would look for, it would be a shame to lose that. Access to posts in raw format would be nice in this scenario.

Its not a bad idea to filter content though, and/or have a flag button on threads/posts. 300 million articles from 40 years of an obscure and anarchic corner of the internet are bound to contain posts that are either potentially illegal or which you otherwise don't necessarily want to be publishing.