Organizations do not necessarily require structure, association is a synonym for a reason. Decentralized organizations and associations are a thing. Decentralized workers solidarity movements and co-op/community strengthening initiatives can be/are "organizing" even if no one is in charge. You don't need to be a member of a union or an official neighborhood association to be part of an organization, there just needs to be general or vague common intention among a group and something of a shared identity. You might not get as much done a fast when not structurally organized, but you also don't not exist if your not a card carrying member. I don't understand the desire to divorce Antifa from being an organization or even existing. It's like saying that the Deadheads aren't a real thing because no one was directing the vast majority of fans who packed up and followed the band across the country.