A more effective solution would be to implement HTML tags for explicit sexual content (or any other kind of child-sensitive content) and allow the OS or browser to authenticate the user before showing that content, if parental controls are enabled.
Legal obligations and responibilities become very clear: the site has tags - it's ok. No tags - guilty.
It also allows for very fine-grained delimitation of sexual content. No need to forbid access to an entire site for one page, or one paragraf of sexual content. Just blur/censor the <adult> ... </adult> content.
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