Funny thing is, writing chan/shota/incest/whatever unethical sex act you can imagine is perfectly legal.* Freedom of speech, y'know. (And yes, I understand that lj, as a private enterprise, has every right to disallow whatever speech it does not like. However we, as paying customers, just as equally have every right to decide we do not like their policies and threaten a massive fannish exodus.)

Bottom line: writing about an illegal act ≠ committing an illegal act.

*Of course, if the work in question is a derivative piece (read: fanfiction) then it becomes not-so-legal, for reasons that have everything to do with copyright and nothing to do with sex. This is true of even the most sparkling, squeaky-clean, smut-free fic out there.