How could you possibly expect to control people saying things about your blog on a remote webserver?
There is no solution that is not worse than the speech.
This is not a problem that needs solving.
It's called Aether, and it only supports text. Each node stores 6 months of all posts. Every person votes for their own moderators of communities so you can basically choose your own moderation filter that you get.
I didn't personally like the idea that it has amnesia after 6 months, but surely eventually clients would support saving your own threads to keep locally.
So you could subscribe to your own trusted adblocking/flagging list.
You're right. My point would make sense only in case of an opt-in solution.