I'm not a part of the Harry Potter fandom, but I've been hearing about this
fandom_scruples thing for several days now.
So I wandered over and took a look just to see.
My opinion:
In the United States of America, first ammendment rights protect Freedom of Speech.
NC-17 fanfic (graphic depictions of sexual acts) are not much different than your standard trashy romance novel.
Therefore, I will place a password code on my NC-17 fanfic when bookstores place a padlock and an age verification system is installed on the section of the bookstore containing books depicting graphic sexual acts.
Rating systems on fanfiction are purely voluntary. Ratings are required for movies and video games (and sometimes music) for mass distribution, but guess what folks! That's not required for books. Yes, some will be sectioned out for purely adult content, but throw in a plot and it can be housed on the shelf next to the Bible.
If we put an NC-17 label on a fic, we've done our part. We're appropriately taking the opportunity to warn audiences about content (because it is very widely realized in fanfic communities that the NC-17 doesn't refer to violence).
If you can't take the time to set up a Net Nanny, then don't try to make me set up passwords and locks. You are responsible for what you and your child view. Stop being a lazy ass and start being a parent and responsible.
Thank you and have a nice day.