[bsdetector]

The cost to the content provider can be reduced to zero by the parents, by allowing it in parental controls.

So the maximum cost to a provider is capped at convincing parents to disable blocking of the content. That could be an unfathomably large sum for pornhub or negligible for wikipedia.

The question then is what's cheaper, paying to have parents enable the content (for instance advertising to make that choice acceptable) or rating the content? If it's the former that's essentially the same value parents place on blocking that content.

You're looking at rating content in this default-block scheme as a cost, but really it's a discount. You're paying a smaller amount to rate the content "G - general audience" then convincing parents to allow unrated content.