This sounds very similar to PGP if everyone had chosen to use it comprehensively for every conversation. Adoption, proper key management, and ease of use were

This sounds very similar to PGP if everyone had chosen to use it comprehensively for every conversation. Adoption, proper key management, and ease of use were the killers there. Social karma style scores are trumped by giant clusters of spambots building up a huge collective karma and then infiltrating existing networks at the edges by phishing or buying existing accounts/keys. Also, some people turn nutjob and then you need a way to go back and revoke all your permanently-recorded cryptographically signed likes and follows because anything less would allow censorship. Not to mention the cost of re-running pagerank over the entire internet population on every client for every new (un)like/follow. People who abandon their keys leave permanent positive karma sitting around for exploitation. If karma is only positive then pure abusers have no negative signal and can coast on these abandoned karma edges. If you allow negative signals (publicly signed "block"s, "this is spam" judgements, etc) then spammers have a new weapon to kill off every other high-karma key with negative edges to reduce its spam-fighting effectiveness. Don't forget that this kind of battle will also be waged by otherwise highly-rational political actors whose survival depends on curating high karma keys and cliques to bolster then. What works is human moderation in highly functional online communities. Read the excellent posts by dang here about his ethos and practices. Human communities are too complex for algorithms or models to manage, at least so far.