This actually happens in the original Freenet (now Hyphanet): the communication tools use propagating trust and blocking. So if someone you communicate with regularly sees something objectionable and blocks it, it disappears for you, too.

But you can always create a new identity that does not trust the other person — or set your own local trust — to see the content anyway.

The important point is that this way resistence against disruption of communication scales better that the disruption (spam, libel, harassment, ...).