"Many books have now been fixed..." so they're still intending to use this filtering code.
As an option "Eliminate items with these tags from my shopping experience," fine. I'm not interested in erotica myself. But that should be a choice left to the user.
(And, by the way, kids can have Amazon accounts, with or without a credit card. Mine have both had accounts for years. The question really is, at what age do you let kids use computers unsupervised, and how often do you talk with your kids about what's online? For that matter, at what age do you let them go to book stores or the library without supervision?)