Regardless of technical viability, any service without moderation is a service mainstream society will shun, which really just means people won't use it, build tools for it, or generally accept others who use the service. People seem to both want a service that is immune from society and also used by society. That's a conflict that won't resolve.
Fortunately, the problem you're talking about has already been solved with the concept of federation. If the social media system is a protocol and not a company, then society can chase down individual bad actors, and blame them for their own crimes, instead of blaming you.
Just the last week a musician tweeted something dumb about making his daughter learn how to use a can opener to open beans, and within a day, the very successful podcast he did the theme song for, where his track was used for the past like 10 years disowned him and stopped using the song. Then he was kicked off the cruise gathering where he was good friends with the guy who ran it and has been a regular headliner for years.
The internet has created a culture problem that I'm not convinced decentralized social networks will fix. At best, if one was created that people actually used, we wouldn't have situations we've seen with Alex Jones and Trump where all the platforms unperson someone on the same day, cause they could still at least keep their audience on the decentralized platform.