So let's get into the real backbone of that essay, the real reason I wrote it. That is simply this: Rowling is writing postmodern literature, telling us a story that deconstructs another more powerful, oppressive story.
The key to understanding postmodernism and what Rowling is doing is getting a handle on the word metanarrative. A metanarrative is any overarching story about The Way Things Really Are. In short, it's a story that tells us what reality is really like. To illustrate, we can take the extreme example of Hitler, whose German supremacy was the metanarrative driving the actions of the German government and military. Those who did not follow the story were trampled upon. We can even find traces of metanarrative in the rhetoric of our own president. When President Bush speaks of freedom and democracy being the goal of history, the real place where history is headed, he's using metanarrative talk.
Metanarrative is rooted in Enlightenment thinking (though metanarratives certainly existed prior to the 1700s). The Enlightenment Project taught us, in layperson's terms, that we all have excellent rational faculties, and if we all apply them, we'll arrive at a universal reality. In other words, we'll all, of our own rational capability, come to the right code of ethics, the right morality, the right way to treat our fellow humans. The problem, of course, became quite evident: After a few hundred years, not everyone agreed, and to complicate the problem, those who were in power used that power to silence the minority points of view. Suddenly, in the words of Voldemort himself, "there is no good or evil; only power, and those too weak to seek it."
Because that's what metanarratives basically boil down to. If I think reality is one way, and you think it's another, and I've got a gun and you don't, my reality wins. French philosopher Lyotard has defined postmodernism (admittedly, "simplifying in the extreme") as "incredulity towards metanarratives." Certainly, it is much more than that, and you learn from reading the likes of Derrida and Eco that it has a significant amount to do with the nature of truth and language itself. But the driving force behind postmodernism is the injustice caused by the powerful on those who had no power and dared to believe something different, or just be different.
The real problem is not the stories themselves, of course. We all have beliefs about reality that we hold to tenaciously. The problem is when the powerful impose their stories on the less powerful, the minorities, those who are different.
A postmodern writer, then, spends his or her efforts deconstructing </span>these grand, overarching narratives. We've come to learn that we see reality in different ways, interpreting through the lenses of our own cultures; there is no "universal reason" that is driving us all to the same conclusions.
Metanarratives in Harry Potter
So Rowling has set up for us metanarratives in the Wizarding World that parallel the ones in our own, and she's deconstructing them. Now, it should be noted that Rowling is not a pessimistic postmodern; she does believe we can "reconstruct," so to speak, and move from wild cynicism about metanarratives to an ultimately better understanding (for more detailed looks at this, see this post at Muggle Matters, and be sure to read the comment by Felicity as well).
We've already mentioned Voldemort and his belief about power. We can add to that his taking up Slytherin's crusade against Muggle-borns. The belief that only pureblood wizards should be accepted and valued is nothing short of an oppressive metanarrative, meant to destroy Muggles and Muggle-born wizards. Voldemort intends to act this metanarrative out in real history, and as such, the central problem of the Harry Potter series, Rowling's contribution to the Problem of Evil, so to speak, is an oppressive idealogy, a metanarrative.
The Ministry's Metanarrative: Prejudice and Slavery in the Wizarding World
The great irony is that the Ministry of Magic, as well as a large part of the Wizarding World, while hating Voldemort's oppressive metanarrative, is operating on its own. But just because the line of prejudice isn't drawn between purebloods and "mudbloods" doesn't make it any better. The most obvious example of prejudice in the Wizarding World is the fountain, portraying the centaur, goblin, and house-elf regarding the wizard with great admiration. All one needs to do is consider the centaurs' attitude towards wizards to know that the statue is a lie.
Prejudice in the Wizarding World exists far and wide. The fact that there even needs to be a Muggle Protection Act proposed in the first place demonstrates the prejudice against Muggles. We can hear echoes of prejudice in Slughorn's surprise at the talent of certain Muggle-borns and in Ron's repeating the "willing slave" line about the house-elves, which enslavement is in itself another obvious example. Despite some creative theories proposing that the house-elves represent house-wives, and Hermione is a rabid feminist, Rowling has been explicit in saying that the house-elf story is about slavery:
The house elves is really for slavery, isn't it, the house elves are slaves, so that is an issue that I think we probably all feel strongly about enough in this room already. [original source]
So she's telling metanarratives we know: prejudice, slavery, and even legislative action against those who are different. Consider, for example, the law against underage wizards using magic. This is nothing short of institutionalized prejudice against Muggle-borns, because, as Dumbledore explains in the spider-infested shed at the Weasleys, the Ministry only knows that magic was performed, not who performed it. It would be impossible to prosecute an underage wizard born to a witch and/or wizard, unless the parents were really honest and willing to turn their children in. In short, it's a law that prevents muggle-borns from developing their talents during the summers while turning a blind eye toward established wizarding families.
And then there's the wand issue, which is the inspiration for my Ollivander essay. The law forbids non-human magical creatures from carrying wands. There is plenty of canon evidence that both house-elves and goblins could use wands (Winky, for a house-elf example; and Harry's OWL question is about goblins and wand restrictions), and we should assume that the law is not arbitrary: it's obvious the Ministry is afraid of the goblins, and the house-elves have been oppressed for centuries. Banning wand use for each group is for the manifest purpose of maintaining wizarding superiority.
In short, banning wand use maintains the Wizarding World's metanarrative that Wizards are better than all other magical creatures, and that, indeed, the entire rest of the magical world looks up to Wizards.
Dumbledore the Deconstructer
Albus Dumbledore does not wand to be Minister for Magic. He's been offered the position three times, and continues to turn it down. Why? Because he is our postmodern deconstructer. He's the one tearing down the false wizarding metanarrative. Consider the following:
Dumbledore employs house-elves and pays them if they want it. He does not demand respect of them as their usual owners would. He does not even demand that they always speak well of him; they may call him a "barmy old codger" if they'd like. As I argued in my Ollivander essay, House-elf life at Hogwarts under Dumbledore is a transitional period toward the hope of their future freedom (a hope that I think will get some wings and take off in book 7). Dumbledore agrees with Hermione's views about the enslavement of the house-elves; he just has a different and more sensitive way of working for their freedom.
Dumbledore maintained good enough relations with the centaurs, who hate wizards, to have them show up and pay respects at his funeral. His hiring of Firenze must have been simply scandalous.
Dumbledore has accepted all sorts of "questionable" wizards, giving trust, acceptance, and second chances: Snape, a repentant Death Eater; Lupin, a werewolf; Hagrid, a half-giant; Mad-Eye Moody, an ex-auror gone a bit senile; Trelawney, an obvious fraud; Firenze, a centaur; Draco, offering redemption to his would-be murderer.
Dumbledore entreated Fudge to "extend [the giants] the hand of friendship;" otherwise, "Voldemort will persuade them, as he did before, that he alone among wizards will give them their rights and their freedom!" (GF-36). Once again, scandalous as far as Fudge was concerned. Two points are important from this exchange: (1) It's obvious from Dumbledore's argumentation that wizards have denied the giants their rights and freedoms, and (2) Fudge's response, that people hate the giants and it would end his career, demonstrates plainly how widespread the prejudice is.
Dumbledore, from the start, has been the voice of tolerance, love, and acceptance. When Rowling wrote him as "the epitome of goodness" [source], she meant it. He is the representative for the deconstruction of the oppressive Wizarding World metanarrative.
I am agreed with Merlin that writing Dumbledore as manipulative is over-deconstruction. He sums it up beautifully here:
Dumbledore himself acknowledges making mistakes in regards to pairing Harry with Snape for occlumency lessons and not taking into account the impact their history will have on their ability to work together on it, and errors in judgment etc But to take it to the level that it sounds like it is being taken in some of the theories talked about, sounds like the deconstructionism is being taken too far, to the level where one has to deconstruct/discount the character responses to DD by other genuinely downtrodden and genuinely good characters (and ones who seem pretty discerning at that, I mean Lupin was able to approach Snape with thankfulness for the WB potion even though Snape exposed him in the end, and if all our "good Snape" theories are right, it would seem that Lupin at the Burrow is more right than he is at the end of HBP)
Dumbledore refuses the MoM position because he refuses to be part of the problem, and the corruption throughout the Wizarding World is far to extensive to simply assume the power of Minister for Magic won't tempt one to compromise. No, better for Dumbledore to advise, and when necessary, criticize the Ministry from the outside, all the while raising up a new generation of wizards and witches, hopefully teaching as many of them as possible to abandon the old prejudices that result in oppressive metanarratives.
Reconstructed with Love
When the Ministry that is fighting Voldemort is bound by the same idealogical problems as Voldemort himself, what is a wizard to do? Like Harry, become "Dumbledore's man through and through." Stop scoffing, as Voldemort did, at the idea that love is the most powerful form of magic, and embrace the idea. The destruction of the fountain was a poweful symbol of the deconstruction of the Wizarding World's oppressive metanarrative; it is to be reconstructed with love. It is no coincidence that Dumbledore insists "love" is "the power the Dark Lord knows not."