@chitty, it's rather a tricky area, isn't it? As you hinted at, connecting and communicating is a fundamental part of human systems that seek to "organize" something. And I think an important point to keep in mind here is that "cooperation" isn't necessarily the same thing as "collusion," and cooperation doesn't necessarily lead to collusion.
As far as I can tell (and granted, I am NOT an expert!) the Achilles heel of decentralization is the risk of "fragmentation." When we put too much effort into making sure nobody (or group of nobodys) holds too much power we also run the risk of squelching positives like cooperation and "economies of scale."
In a sense, it's a bit like a farmer's market... both the growers AND the public benefit from everything being in one place. But that also means we have to have a set of (dread!) common "rules" or "guidelines" and includes the risk of "factions" aligning under common interests. But we put up with it, because it really SUCKS (as a user) to waste all day going to 17 individual farms ("fragmentation") to shop for dinner.
Again, this is overly simplistic.