Growing up with the Star Wars movies, I had always considered the Jedi Knights as heroes, with Luke Skywalker and Ben Kenobi as the prime examples of that. My first inkling that the Jedi might be somewhat fallible was in the Empire Strikes Back, with the hesitation of Yoda in taking Luke on. And then again, in Return of the Jedi, when Yoda and Ben are revealed to have been keeping secrets from Luke. In essence, they were manipulating him to do what they wanted, afraid that if he knew the truth, he might not 'do the right thing'. In the end, everything turned out alright, but it did impress upon me the fact that the Jedi were not entirely the bastions of light and goodness that I was initially led to believe.
My next interaction with the Jedi was when the prequel trilogy was launched in 1999. Once again, the Jedi are presented as heroes, but especially here, you can see the cracks appearing in that facade. For all their might and power, things are happening behind the scenes that they are unaware of. And when Anakin is discovered, the Jedi are both dismissive and (seemingly) frightened of the prospect of this prophecy. For all their philosophizing and wisdom, rules and codes, they seem to be reacting with very 'human' emotions.
All of these perceptions only deepened as the prequel movies continued—and especially in Attack of the Clones. Here, we hear Yoda talking about how the Jedi have grown to proud and many of them are 'losing touch' with the force. We see arrogant Jedi librarians believing that anything not in their records does not exist. We see equally arrogant Jedi warriors, bursting into the Geonosian arena without immediate backup, and falling into a deathtrap. We see them following along blindly in accepting that someone (apparently one of their own) just built this Clone army that just happened to be handy the moment they needed them (hmm, convenient). And we see them not understanding, or wanting to understand, just what this prophecy of "Bringing Balance to the Force" means.
And then, even before Revenge of the Sith came out, the Knights of the Old Republic video game series arrived on the scene. In the narrative of both of these games, the Jedi come off as somewhat troublesome allies. Some are noble and forthright, but others are outright bitter and even hostile. As with the movies, it shows the Jedi in a period of decline and turmoil, and in the final game of the series came the big revelation to me: The Jedi were essentially the bad guys. They had become so caught up in their own teachings that they could not understand how someone (the Jedi Exile) could function—could succeed—without the using the Force as they knew it. In fact, the Jedi actually try to KILL the hero of the game because they don't understand what that hero has become.
And finally, in Revenge of the Sith, we see the ultimate fall of the Jedi. They allowed themselves to be led along, sure in their own abilities. They allow themselves to be spread too thin—and put in front of an entire army of troopers who's too-convenient existence they had never questioned. Too late they try to understand the prophecy of "balance"...and this ultimately turns out to mean almost literally what it says: At the end of the trilogy there are two main sith and two main surviving Jedi. Yep. That's balance for you.
In the movies and the KotOR series, it seems to be a classic case of power corrupting. The Jedi bought into their own infallibility, and that is why they fell. The KotOR series central theme (to me at least) was this: Jedi have to remember and even embrace the fact that they are still people. Yes, its best to try to act on rational thought, to not let your emotions cloud your judgement—especially in combat or high-stress situations. But (in my opinion at least) it is the positive emotions (love, friendship, hope, compassion) that are the true source of power—for Jedi or anyone. By divorcing yourself from those kind of emotions, you remove yourself from the world around you and you begin to lose touch. I think that this is exactly what was shown in the movies and the KotOR series—in both cases, it was emotion that ultimately carried the day. Simple, positive emotion.
And so, the Jedi as Villains really got me thinking (as you can tell from the above). The whole idea of it really adds depth to the usually black-and-white universe of Star Wars.