In practice I don't think it's an issue. What I'm arguing for is the infra to facilitate self categorization and (likely) also a legal requirement limited to only a few specific categories. For example the government might mandate that porn, social media, and user generated content all be accurately tagged and provide legal definitions.

Nothing about what I describe would preclude additional layers of categorization such as (but not limited to) whitelists. In fact it should improve such efforts by providing a standardized method they can use for arbitrarily fine grained categorization that will be compatible with other software out of the box.

Note that my tagging proposition could be applied per network request. So if the service operator wants to it should facilitate filtering out (for example) a comment section without blocking access to the rest of the site.