I moved to Diaspora after Google Plus was killed. It's mostly good, if small, but with one really big problem: you can block trolls, but trolls can always create new accounts and come back.

It's probably impossible to create a decentralised social network where don't constantly have to reblock the same trolls but also don't get locked into a tiny closed community. I want to be able to talk and share with the whole world, but I don't want to have to block the same assholes over and over again because they keep making new accounts. And I assure you that trolls can get pretty bad on any open, decentralised system. They certainly do on Diaspora.

Maybe something where your network only expands through trusted nodes in your network: if a friend follows a lot of trolls, maybe keep him as a friend, but don't allow your network to expand that way. But someone else might follow a lot of interesting people, so open up your network a bit more in that direction.