I think this is a serious problem - but probably not for the exact use case you list (mafia, sexually abused kids).
It should be solved by allowing an "expensive" (a) "vote" (b) to override, or delete, or hide for a number of years.
(a): expensive should discourage the option in general
(b): proof-of-stake, proof-of-ownership, proof-of-work are some of the many ways in which you can define voting rights.
Unfortunately, it doesn't work easily in practice. Example:
You created a file (say, a CV, or a newspaper article in PDF) to discredit me, but it's a lie. To me, not having that file publicly accessible would be worth $1,000.
You could blackmail me - give me $1,000 or I'll upload the file! But I think you might do it anyway, so I don't negotiate (never negotiate!!).
The file is 1 MB, and it costs $1/year to keep it up and running on Filecoin.
I should have an option to ask a voting pool to remove that file for $100. The pool agrees, and the money gets burned (I shouldn't create any incentive for someone to cash in the amount).
However, you can upload the file again; or a slightly different version, and we are back to square one.
It then goes to the "discoverability" of the file. That part is probably going to be decentralized too, so no court could "order" Filecoin to make a file not discoverable.
How do we solve it? I think there will emerge a search system that provides services to censor, obfuscate, etc, a number of files, based on reasonable requests. Whoever builds that company, I bet it will not be poor.