What we need is a mechanism for breaking circuits of lies and propaganda. In real world social networks we have methods like labelling liars(You have one identity and you risk it every time you say something), right to defend yourself(You can actually identify and force your way to reach the people who are exposed to, or facilitate it) if you are being smeared for or accused of wrongdoing. You don't have these mechanism in the digitalised version of social networks. Social networks work like cults, your reply to an online mob at Twitter/Instagram/Reddit/FB etc. reaches no one else but your own cult(if you have one).
Oh and believe me, lies are dangerous. In istanbul there are many abandoned beautiful buildings in central locations, many these belong to Greeks who lived in Istanbul for generations but in 1955 were targeted by the Turks who were told by a newspaper that the Greeks bombed the Turkish consulate and Ataturk's birth house in Greece: https://en.wikipedia.org/wiki/Istanbul_pogrom
There was nothing centralised about this Progom, the newspaper was not the governments publication like in a Communist dictatorship. Yet, it caused so much pain to the Greek minority and Turkey lost so much as the Greek christian population declined from 120K to 7K in 20 years.
If anything, decentralised networks can be targeted very efficiently by a bad actor and the rest would have no recourse. There's nothing stoping (fascists/communits/liberals/$_YOURBOOGYMAN) to identify decentralised networks, connect to all of them, participate and run a propaganda campaign through a centralised unit that connects to all the decentralised networks.
If there were thousands of decentralised social networks, QAnon could have used Buffer to manage their presence in all of them.