The basic premise was that history's most heinous acts of evil in the fantasy world were engineered by a secretive cabal composed, not of uber-powerful bad guys, but of normal folks (there were a few well-respected rulers, guild masters, and former adventurers involved, but they were the exception, rather than the rule). All were involved for their own reasons, but fundamentally all believed that true heroes - and, thus, true hope - could not exist without true evil to struggle against. And true evil isn't exactly in large supply.
Basically, this hidden cabal - through an elaborate system of financing and influence - sought out potentially dangerous 'would-be' villains, and then anonymously provided them wtih funds, information, and other resources to carry out great evil in the world. Similarly, this same cabal would then arrange for potential heroes to stumble upon these schemes and, again, anonymously supply aid to them (planted magical items, companions hired for PCs to 'accidentally' stumble across, etc).
The rest was then left to fate - some hereos thwarted the evil while others died trying. In the event that a given group of heroes died, another would be 'recruited' to take over where they left off, until the evil was eventually undone in a spectacular show of heroism that the public could admire. There were, of course, 'fail-safe' measures in palce to ensure that said evil never got out from under the cabal's thumb (they could withdraw resources, quickly turning that Big Bad back into a minor foe).
The campaign itself used this cosmology to explain the otherwise glossed-over origins of the numerous larger-than-life heroes and villains in various D&D settings, and gave the PCs a truly warped (if well-meaning) world-wide network of baddies to rally against - if they ever discovered its existence (many PCs were content to not question the nature of evil, and were happy to smite whoever the cabal dropped in front of them, never becoming aware of said cabal's existence).
The road to Hell is paved with good intentions and, in the end, the cabal ends up being that true evil that they hoped to create. Que the epic confrontation with the ruling cabal members. All in all, a lot of potential for a memorable campaign, IMHO.