This is the correct answer. Since it was a "permissionless publish" system, with no authentication, anyone could post anything. This was a disaster in the way that pure free speech systems always are.
(To some extent, there was a natural response in that anyone could cancel anything, although those ended up adding authentication. At one point people estimated that a third of traffic was spam and another third was "spam cancels".)
It was always "permissionless publish", but it is worth remembering that it wasn't a free speech system (until alt.*) Each group had a manifest of rules.
I think that the issue was that the enforcement mechanisms were largely social, so they broke down when it grew too large, especially when ISPs and others started running servers without engaging in the community.
