The most important shortcoming of the Harry Potter series is its often unconvincing depiction of evil. Creating a plausible ideology for the “bad guys” in a fantasy series is an important challenge that many writers try to sidestep. There are all too many fantasy books that include a “Dark Lord” who seems to be evil for evil’s sake, without any justifying ideology that might actually appeal to anyone. This is an important weakness of many works in the genre, and J.K. Rowling unfortunately falls into this trap in the Potter books.
Rowling does a great job of depicting the negative effects of government and bureaucracy: institutions that are supposedly set up for beneficial purposes, but actually cause more harm than good because of their indirect effects. She is much less convincing in her depiction of the more radical evil represented by Lord Voldemort and his followers. The problem here is the absence of ideology. Voldemort seems to be motivated almost solely by his desire for power and immortality. His followers seem driven either by fear of his power (the Malfoys) or personal loyalty (Bellatrix LeStrange).
Real-world evil political movements simply aren’t like that, at least not exclusively so. They always have an ideology that justifies their policies, usually a quite elaborate one. Think of the Nazis, the Communists, Al Qaeda, and so on. Each of these groups had a detailed ideology that purported to explain why their policies were right, just, and necessary for reasons that go beyond the narrow self-interest of the movement’s leaders. Even if the leaders themselves didn’t always believe in the ideology, it played a key role in motivating and indoctrinating the followers.
Rowling takes a small step in the right direction in her emphasis on Voldemort’s and the Death Eaters’ hostility to Muggle-born (“Mudblood”) wizards. The obvious analogy is to real-world racism. However, she never really explains why the Death Eaters hate Muggle-borns so much, which makes the hostility seem unmotivated and pointless. In the real world, racism and anti-Semitism were justified by elaborate theories of either the inferiority or the malignant nature of the despised group. Often there are also real or imagined historical grievances. We see none of this in the Potter series (at least not on the part of Voldemort and his followers; groups such as the goblins and centaurs do have historical grievances against wizards). This gives a misleading image of the true nature of racism, feeding the modern conceit that it is just the result of “hatred” or intolerance. In reality, the hatred and intolerance are usually the consequences of racist ideology, not its causes. The core of anti-Semitism, for example, is not hatred of Jews in and of itself, but the list of reasons why Jews supposedly deserve to be hated.
In Book 7, Rowling belatedly recognizes this problem, and has the Death Eaters justify their hatred of Muggle-borns by claiming that they supposedly “stole” their magic from “pureblood” wizards by taking wands from them. However, this claim seems utterly implausible as a basis for Death Eater ideology because it is too easily falsified by everyday experience in the wizarding world. As was established early in the series, virtually all wizards know that the ability to do magic is innate, and cannot be acquired simply by taking a wizard’s wand. Real-world ideologies, however absurd in their ultimate conclusions, have to be sophisticated enough to avoid falsification by the basic facts of everyday life. An effective ideology must have at least some plausibility.
The prevalence of essentially nonideological evil in fantasy literature is unfortunate. It leads to a,cartoonish distortion of the way evil wins adherents. On balance, the many virtues of Rowling’s books outweigh this one defect. But it is a defect nonetheless.
UPDATE: Steven Bainbridge has an interesting response to this post. He argues 1) that Voldemort doesn’t need an ideology to motivate his followers because they are only a small group, and small groups can be effectively motivated by other means, and 2) tht Voldemort does in fact have an ideology based on the need to protect the genetic basis of wizarding ability from dilution through intermarriage with Muggles. Regarding the first point, I entirely agree that small groups are easier to motivate by nonideological means than large ones. However, small groups that seek to overthrow and entire social order usually do develop an ideology nonetheless. The Communists, Nazis, radical Islamists, and others all started as very small groups, yet all had an ideological basis from the start. Moreover, Voldemort is clearly seeking to gain the support of the wizard population as a whole, not just a small group. That is why he puts out propaganda (as Bainbridge himself points out). Persuading large groups does require an ideology of some sort, as Bainbridge concedes.
On Bainbridge’s second point, I think he has indeed come up with a plausible ideology for Voldemort (relying on this essay by another Harry Potter commentator). The problem is that this ideology is nowhere mentioned in the books. If this were the real ideological rationale used by Voldemort, one would think that J.K. Rowling would have mentioned it somewhere in the several thousand pages she wrote for the series. Certainly, she has lavished attention on many far less significant details of the wizarding world.