Greedy, Cowardly Ferengi
In "The Last Outpost", we were introduced to the Ferengi. Gene Roddenberry originally envisioned the Ferengi as the Federation's primary foe, to take the place of the Klingons and Romulans. This was part of the sea change in Star Trek's underlying theme, which was being revised from the 1960's Cold War to a left-wing liberal tirade against consumerism and capitalism. But the Ferengi were not simply greedy; they were powerful, mysterious, and dangerous. The very first Ferengi warship we ever saw was powerful enough to dice with the Federation's biggest, most powerful battleship, and its crew was highly aggressive. Despite their small stature, they were able to surprise and defeat a Federation landing party on the ground. Their appearance may have been odd, but these were clearly not people to be trifled with.
When they reappeared in "Peak Performance", they were similarly threatening. They dropped out of warp at point blank range, opened fire on the USS Enterprise, and promptly disabled most of its combat systems. They demanded the surrender of the derelict USS Hathaway, and when Picard (seemingly) destroyed it rather than surrender it, the Ferengi captain grudgingly complimented him by saying that "I did not think the Federation had such iron!" A rather warrior-like sentiment, is it not? Similarly, Picard once recounted the story of how he lost his previous command, after his ship was reduced to a flaming wreck by a Ferengi warship. This is a far cry from the cowardly Ferengi of DS9, isn't it? But in every appearance, the Ferengi made reference to a profit motive, and that was more than enough to plant the brain bug.
By the time the Ferengi showed up on DS9, their interest in profit had grown to encompass their entire culture. They were suddenly interested in nothing but the accumulation of wealth, and the writers' desire to simplify every alien society into a one-note joke meant that any non-financial elements of their society (including the strong martial tradition that was obvious from their initial appearance in TNG) vanished without a trace. Now, they were a laughingstock in combat, and they made frequent disparaging references to their own combat ineptitude. When Nog elected to join the Federation military, the decision was treated with shock, contempt, and derision by his relatives because Ferengi are businessmen, not soldiers. When Quark went on a mission to rescue his mother, they found a single Ferengi mercenary who was good with weapons, and the others acted as if he was some kind of freakish anomaly. What happened to the heavily armed Ferengi warships we saw in TNG? Did the writers suffer a massive collective amnesia attack?
As time went by, this brain bug continued to grow. Not only was greed now the only defining characteristic of Ferengi society, but the writers figured they were on a roll, so they even made it the Ferengi religion! Instead of the Ten Commandments, the Ferengi had the "Rules of Acquisition", with which the viewers were bludgeoned with constant reminders of Ferengi greed. Instead of "astral plane" or "holy ghost", they had the "Great Material Continuum". We were told that the Ferengi had no loyalty to anything but money; not to friends, not to family, not to king and country. No one ever managed to explain how a society could possibly function along these lines, but no matter; the writers obviously had no interest in constructing an interesting or multi-faceted alien society for the Ferengi. Far from it; instead, they seemed to be interested in reducing it to a single element, just as they had done for the Klingons. By the time they were done, another society had been transformed into a farcical one-note caricature by the unfettered growth of a brain bug. Planted in TNG, and grown to the proportions of Jack's famous beanstalk in DS9.
