Man's capacity for evil is as well-versed a topic in literature and film as the good/evil divide itself, and the enduring appeal of the age-old story is precisely why we've seen hundreds of variations of the Frankenstein tale of unwittingly created evil. Heroes invariably create their own opposites, or at least draw them out (something that is ingeniously played with in Unbreakable), and though that dynamic is an enduring one, sometimes the creation of those villains comes down more to idiocy than virtue.
It is the ultimate irony that in seeking to make a better place and get rid of malevolent forces, heroes occasionally manage to drop the ball so spectacularly that they engineer their own doom - or put themselves in extreme danger at least. And they aren't the only ones: super-villains often unwittingly create the means to their own destruction, concentrating too much on their grand plan to notice that they've just turned a pawn, or an innocent bystander into a future harbinger of death or defeat.
Whether their intentions were good or for evil, the single unifying point here is that these characters - most of whom are usually intelligent, and efficient - made some bad decisions and ended up directly creating the people who would go on to almost ruin their worlds completely.