As someone who has spent the better part of their life advocating for openness, decentralization, etc... it pains me to believe this, but I'm not sure we can have both open decentralized communities and simultaneously a community that isn't overrun with toxicity.
If the goal is shitposting and edge-waddling I think it can be done, for a while anyway. However, if the goal is to have a space where discussion is meaningful, good faith, charitable, intelligent conversation, I'm not sure we can currently do this in a completely open way and still maintain a signal to noise ratio where sane people would willfully spend their valuable free time.
In our current iteration of tech, society, education levels, culture, and politics it seems that (so far) every time we create an open space, the moment it reaches a certain level of popularity, the noise levels reach a point where it is pretty much impossible to have meaningful, contextual, and nuanced conversations.
At the point that signal to noise ratio reaches unacceptable levels, we lose a critical mass of the people who made the space "special"
I really hope we can get around this someday, but sadly, so far the absolutist free-for-all spaces really offer diminishing returns for those of us who are busy. Rather than sifting through rubble to find gold, at least for me, I can think of many things I'd rather do than engage in a conversation with someone when there is a higher than average chance they aren't there in good faith and when entire segments of the community exist who are literally only in the space to engage in and spread sophistry.
At least for now, outside of invite only communities or high barrier of entry communities, spaces such as HN or SSC --both of which are largely unknown to the general public-- seem to offer the best blend of openness and time-well-spent conversations. But I'm not sure either of these could maintain the same level of conversation at scale.