As an example, yesterday afternoon we were enjoying a midday snack at a local restaurant. Enjoying the emptiness of the venue, we decided to discuss matters of great importance to us: namely, what the retention rate for muggle-born students at Hogwarts might be. Obviously, they can perform magic just as well as pure-blood/half-blood students (shout-out to Hermione Granger & Lily Evans Potter, eh?). Lily is nigh on deified in the story. And Hermione's knowledge of the wizarding world could put some pure-blood brats to shame.
But where are all the "first generation" muggle-borns? Lily Potter seems to be the exception rather than the rule in Harry's parents' generation. Most of the mentioned characters are either half-blood or pure-blood. There are a handful of older muggle-born witches (Kendra Dumbledore as one possibility), but very few of them are active characters in the world of the novels. It wouldn't be unreasonable to assume some of those muggle-borns simply hid their heritage to be more accepted in a highly prejudiced society.
But I cannot help but wonder. How many muggle-born witches and wizards might have existed who simply chose to leave the wizarding world behind, either during Hogwarts or shortly thereafter? I am sure there are many individuals out there who know better than I do the details of the books and will probably knock me right off my pondering stool, but I do wonder why there isn't more visible evidence of their existence in the novels.
I once read a fan fiction in which some of the most prejudiced of Hogwarts students were given the opportunity to describe the reasons for their prejudice. One Slytherin argued that muggle-born students rarely fully adapted to the wizarding world, so they eventually returned to the muggle world to make lives for themselves. Their presence at Hogwarts, therefore, only endangered all wizarding kind by making discovery by muggles more possible. Obviously, I'm not the only person who has wondered where the heck all these muggle-borns went.
Perhaps J.K. Rowling was making a statement about the invisibility of oppressed minority groups in inherently prejudiced society. Perhaps she meant something even deeper. Perhaps she meant nothing other than that there were fewer muggle-borns than pure-bloods or half-bloods.
The point is, fans of well-done fiction can take an author's words and glean a great deal of insight--erroneous or not--about what the author might have meant, what he or she might have intended by laying out particular details in a work. J.K. Rowling doesn't hide the wizarding world's general disdain for those born to non-magical parents, yet the attitudes of her heroes tell us a great deal, not just about the wizarding world, but about own her beliefs regarding prejudice in the real world as well.
When writing all fiction, but particularly allegorical fiction, I think it's important that we as authors pay attention not only to what we do say explicitly, but also to what we don't say. How sharply divided are the "good guys" from the "bad guys"? What makes the bad guys bad? Have we portrayed them in a way that might negatively (or positively) reflect on certain groups of people in the world "outside the book"?
I leave you with a copy of a video that went viral a while back: "To J.K. Rowling, from Cho Chang." Whether you agree with the poet or not is irrelevant to the point. What's more important is what Rachel Rostad read in JKR's work. What strikes me most about the piece is how a poet, more sensitive to cultural issues surrounding the ethnically Asian community than JKR could be, makes an argument for racism in something as simple as a choice of character name. She makes other valid points as well, but that one argument almost cinches the deal for me.
I highly doubt J.K. Rowling set out to be known as racist against any community. Most of the series seems to be about the futility and danger of harboring ridiculous prejudices. Yet her choices hurt a group of readers who needed her understanding and ended up feeling left hanging.
We would do well to learn from this example. You can never have control over what a reader thinks of your work. And there are indeed readers who will take offense at any portrayal they disagree with simply because it challenges them. Challenging readers is GOOD. We shouldn't write only to confirm what others believe is true. We write to entertain, to entice, but also to educate, to force others to think.
Still, we all should do our best to mitigate critics' misunderstanding of our intentions. Our work should say exactly what we intend it to say, even when we remain silent.