you don't need any keys for trust, you can imagine a centralized system and "trust" can be expessed as "adding person to your friends list". Then you the social network recommends you posts of the friends of your friends
what I'm trying to say, I think you don't need public keys to organize content filtering
and to answer the titular question: I don't know such a community. maybe it's possible to use an existing social network and add extra javascript on top to filter posts based on your "web of trust"?
> you don't need any keys for trust, you can imagine a centralized system ...
I guess part of the essence of what I was trying to describe was that it's non-centralized. Otherwise, you have to trust some entity to unilaterally behave well, now and forever. But fair point; something like this could be implemented in someone else's walled garden. I wouldn't trust it though :p
Famously, there have been cases of reddit admins modifying people's comments secretly. A digital signature would defeat that (even if it's hosted on "hostile" servers).
Since you mentioned JS overlays... One thing that is somewhat similar is using RES[1] on reddit. When you upvote/downvote a person's post, it keeps track of a total +/- count for each username, and displays it next to it in the UI. This isn't quite trust, but it is a kind of "my opinion of this user, gathered over time" overlay... There's also no notion of sharing this info with others.
I still feel kind of disenchanted about technology. A founder who punishes and fires employees who delete and modify comments can create a decent website faster and easier. Without any cryptograpghy.
And, since the website also has a reputation of its own people won't want any of the cryptography if they trust the website
The only downside is when the website owner dies eventually it can all go to hell, it's hard to enforce your principles after the death.
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reading your comment again, I think you want to much: you want to see less lower-quality posts and the solution has to be decentralized. I think just not visiting social media can improve your daily life. If only I could follow my own advice though...