In the age of the smartphone, one might be forgiven for thinking attempts to ban books are one of those old-timey things we can all laugh about today, like prohibition or child labor. Yet, every year the Office for Intellectual Freedom (OIF) puts out a list of the most-challenged books in America, based on reports sent in to the office and a review of media mentions.

The fact certain small-minded people still think books filled with ideas are somehow dangerous is only slightly less amazing than some of the reasons they come up with to have them banned in the first place. And as it’s ideas we’re talking about, it’s no wonder many of the books folks try to ban are sci-fi or fantasy—genres that deal in exciting, disturbing, and sometimes downright weird ideas. Here are the 10 most-challenged SFF books of all time.

The Giver, by Lois Lowry

Lowry’s classic children’s novel is usually challenged for similarly classic reasons: its themes and motifs undermine authority. The story of a society where all the art and ideas that are useful but dangerous are held in the mind of single citizen—who then passes them on to a selected heir—also deals brutally with concepts of managed reproduction, sending some folks into a tizzy. But the main reason it’s so frequently challenged is because it can inspire readers to question what information is being withheld from them, and why. Adults like nothing less than smart kids demanding to be told the whole truth.

The Witches, by Roald Dahl

Roald Dahl is a fascinating figure, a man who was difficult to like in real life, whose fiction ranged from dark adult stories to even darker dark children’s stories. Although many of Dahl’s books are subversive, most aren’t obviously subversive, and thus get a pass from the bluenoses who like to ban books; for example, Willie Wonka is something of an ominous character, but the superficial charm and whimsy of the candy factory gets the book a pass. The Witches gets banned because it’s a pure Dahl book, which means it’s a bit dark for the kids it’s aimed at—but also because it contains witches. All it takes for a book to be challenged is a hint of the occult or a whiff of satanism—and so every year, The Witches makes a list somewhere.

A Wrinkle in Time, by Madeleine L’Engle

The word “witch” once again rears its ugly head, as there’s very little in this book that could be regarded as subversive or dangerous—unless you consider awesome, mind-bending ideas and challenging scientific concepts dangerous (some people totally do). But it’s often the simple presence of the word “witch” in the story makes people to try to ban this book, and as it remains so popular, it continues to appear on the most-challenged list year in and year out. The fact that it’s one of those books that both kids and adults can read with equal pleasure doesn’t help, because some folks imagine kids’ books should be innocuous, fluffy confections without conflict, sadness, or, you know, ideas.

The Handmaid’s Tale, by Margaret Atwood

On the surface, the reasons for trying to ban The Handmaid’s Tale are numerous: sexual content, rape, and violence. Under the guise of protecting the innocent from these dirty concepts, though, is the real reason: the howling feminist themes in a story set in a dystopia in which an entire gender has been stripped of its agency and rights, rendered into breeding stock. No one, male or female, comes away from reading the novel without serious doubts about the society we live in right now, in which the role of women in is still in flux in many of the darker corners of the world (and the United States). Questioning of the status quo is reason enough for some to seek to ban teenagers from reading it—lest they get too many ideas.

Flowers for Algernon, by Daniel Keyes

Sometimes it really is the small things. There are brief sex scenes in this harrowing novel of loss, in which a man of very low intelligence undergoes a procedure that raises his IQ radically—but only for a time. The sex isn’t particularly shocking or explicit, but simply because the book is often taught in high schools, it gets challenged on a near-constant basis. Add in the fact that the protagonist has a second sexual encounter that means very little to him, and it’s easy to see why folks might think the book is promoting a lifestyle that could eventually destroy all of civilization.

The Harry Potter Series, by J.K. Rowling

It was inevitable; the Harry Potter books were name-checked in Jack Chick’s tracts for opening a doorway to hell, and as the series became more and more popular, it was also more and more challenged by parents seeking to shield their kids from its supposedly occult and nefarious influence. Luckily, their feeble powers were no much for the sheer marketing and sales powers of the world’s most popular book series, so attempts to ban them were largely symbolic. And while we all learned at least one or two really useful spells reading them (we’re still trying to get alohomora to work right), so far no one’s offered to buy our souls.

Brave New World, by Aldous Huxley

Sure, let’s try to ban a book more or less universally recognized as a work of genius! On the one hand, Huxley’s vision of a future where sex is purely recreational, in which several fairly explicit sex scenes can be found, would seem to be an obvious target. On the other, the book is often challenged for other reasons—including the perceived negativity of the story, bringing into question whether it’s okay for a book to make you think unhappy thoughts or not. We would argue that making you think thoughts—unhappy or otherwise—is the chief goal of any book worth it the paper it’s printed on.

Slaughterhouse-Five, by Kurt Vonnegut

Once described as “anti-American, anti-Christian, anti-Semitic, and just plain filthy,” Vonnegut’s classic novel about a man who becomes unstuck in time and begins flitting across his own life like a tourist is still one of the most-challenged books ever. Part of it is the profanity, which is impressive. Part of it is Vonnegut’s subversive style and worldview—because he was, in many ways, anti-everything—especially if he could be funny while doing it. Above everything else, it’s a passage where Christianity is challenged for selectively allowing violence that gets the novel challenged most often—because we can’t have anyone actually applying their curiosity and intelligence to serious questions of faith, philosophy, and what it means to be a human being.

Fahrenheit 451, by Ray Bradbury

The winner of the All-Time “Most Ironic” award for challenged books is, of course, Bradbury’s classic about a cruel future where books are burned and people are absorbed by the wall-sized entertainments in their homes. The reasons sometimes offered center on the bits of profanity in it, but of course the real reason is simple: the whole point is to encourage people to question what they’re told by authority figures, and to watch out for “forbidden” concepts and ideas, then question why they’re so dangerous. Bradbury was actually thinking of television when he wrote it, worried the tube was turning people into mindless non-readers, but his short novel has become a symbol of the evil that book banning (or burning) represents.

The Hunger Games, by Suzanne Collins

Collins’ new classic of young adult dystopian literature is often challenged because it can be read as encouraging violence; the argument usually centers on the books teaching kids that organizing brutal orgies of bloodletting is somehow cool. As usual, the real reasons go a bit deeper: the books delve into misinformation and “fake news” pushed out by authority figures to control the population, and then flip the script to shows how media can be manipulated to craft a “narrative” in support of a movement. Any time a book gets people—especially younger people—to question the “conventional wisdom,” it’s almost guaranteed to be challenged somewhere.

What challenged books do you love?