
Because I am a geek who actually went and deciphered it...
According to fanfiction.net and fictionpress.com 's Terms of Service, under Term 5: Author/Poster Conduct, point (d) says that the author cannot upload advertisements, promotional material, ect. and (e) put anything that would disrupt the flow in conversation. It’s under those two points of Term 5 that makes it technically ‘illegal’ to break your story for a comment, and to respond to every review. I use the word Technically because that’s what it is: while the administrators publicly posted the rule that people who do things such as the author’s thoughts, overly long A/N, and polls have the very real chance of their story being kicked off the site, they never changed the ToS to fit it word for word; it was in the News/Updates section of the site, but the rule was decided years ago and it’s word for word testimony has long since vanished.
Argument against this rule, however, is voided by Term 6, which states that fanfiction.net has the right to take away or upload any new terms or postulates at any given time. The rule stated has not since been discarded, thus is still in effect.
However, according to the ToS, if you get a Flame, you can kick the flamer off the site under Term 5: point (a) upload, post or otherwise make available make available any Content that is unlawful, threatening, abusive, harassing, defamatory, libelous, invasive of another's privacy, or otherwise objectionable; and (h) stalk or otherwise harass other users; if the act is repeated. Under that Term, you can also report the mysterious people who report you for their views on an illegal writing or some-such. Unless they had a truly valid argument against an authors fanfic, repeated warnings and/or deletions could be titled under Harassment.