But this is software that is intended to actually be used by humans. It would be a far worse user experience to prohibit the "sex" category but then be shown a

But this is software that is intended to actually be used by humans. It would be a far worse user experience to prohibit the "sex" category but then be shown a rape scene because someone added "rape" as a custom category. This concept really doesn't work without standardized categories. Of course, you could argue that more granularity should be added to the categories, and I don't necessarily disagree. You could even have a directed graph of categories, so that (for instance) "rape" could be a descendant of both "violence" and "sex" and thus rape scenes would be banned if the user banned either violence or sex.