“The point,” says cartoonist Jeff Smith, whose multiple award-winning comic Bone was one of the books that parents tried hardest to ban in America last year, “is that they are trying to take away someone else’s ability to choose what they want to read, and you can’t do that.”

Smith was speaking as the forces of free speech mobilised in the US for Banned Books Week, the annual festival that opens on 21 September and which, in the wake of attacks on acclaimed books from Bone to Alison Bechdel’s Fun Home and Marjane Satrapi’s Persepolis, is taking a special focus on comics and graphic novels this year. The most challenged book of 2013 – the book that received the largest number complaints in schools and libraries across America – was Dav Pilkey’s children’s graphic novel Captain Underpants. Smith’s Bone came in 10th, with the series – described as “one of the 10 greatest graphic novels of all time” by Time – drawing fire over its “political viewpoint, racism, violence”, according to the American Library Association.

“I’ll be honest, I had two simultaneous reactions when I heard Bone was in the top 10,” said Smith. “First, that I was being attacked and I didn’t know why. Then a thought like: hey, this isn’t the worst thing that can happen. A lot of my heroes are on this list. Mark Twain, Melville, Bradbury, Steinbeck, Vonnegut; authors whose work is about something – that do the kind of writing I aspire to.”

According to Smith, this year’s focus on comics “matters a great deal”.

“Comics are now part of the literary scene, part of the discussion, and it shines a spotlight on these kinds of attacks,” he said. “That doesn’t mean the people who want to ban these books are malicious; in fact just the opposite. They have a concern which to them is legitimate. But that isn’t the point. The point is that they are trying to take away someone else’s ability to choose what they want to read, and you can’t do that.”

As libraries, schools and bookshops in the US prepare for a week-long wave of events and exhibits on the perils of censorship – since 1990, the American Library Association has seen more than 18,000 attempts to remove materials from schools and libraries – the Comic Book Legal Defense Fund’s executive director Charles Brownstein said that comics and graphic novels were seeing “an increasing amount of challenges”.

“Comics are one of the most commonly attacked kinds of books. They’re uniquely vulnerable to challenges because of the medium’s visual nature and because comics still carry a stigma of being low-value speech. Some challenges are brought against comics because a single page or panel can be taken out of context, while others come under attack because of the mistaken notion that all comics are for children,” said Brownstein.

He cited Chicago public schools’ attempt to ban Persepolis, and the funding challenge in South Carolina that centred on the gay-friendly theme of Fun Home, Bechdel’s memoir about how she came out to her parents.

At the American Library Association, the Office for Intellectual Freedom director Barbara Jones called it a “tragedy” that “some parents, pressure groups and educators remove the freedom to read comics and graphic novels from those who love them and share them”.

“It is a shame that comics and graphic novels take the hit for societal ills like violence and teen drug use, when in fact those (very real) ills are caused by complex social and economic problems like lack of good education and good jobs. Ironically, teens share comics and talk about them – even have school clubs,” said Jones. “Healthy behaviour, I would argue. For some fans, it is their avenue into a lifelong reading habit.”

But it is not only comics which come under attack in the US, and which will be marked by the book trade next week. Over the last year, the National Coalition Against Censorship has defended the right to be read of works including House of the Spirits by Isabel Allende and Rudolfo Anaya’s Bless Me, Ultima; John Green’s Looking for Alaska and Little Brother by Cory Doctorow, as well as Fun Home.

Banned Books Week, which has been running for 32 years, “is a necessary reminder of Thomas Jefferson’s admonition that eternal vigilance is the price of liberty”, said executive director Joan Bertin, pointing to two new trends “of particular concern”: “the effort to censor reading material for older teens, including advanced placement high school and college students, and the increasing tendency of school boards to adopt rating systems to warn parents about books that contain ‘sensitive’ material”.

“School officials may see this as a way to avoid censorship controversies, but it’s likely to have the opposite effect,” said Bertin. “It’s like putting a scarlet letter on a book, encouraging more challenges while deterring teachers from assigning valuable literature.”

The top 10 most frequently challenged books of 2013

Out of 307 challenges

Captain Underpants (series) by Dav Pilkey

• Reasons: Offensive language, unsuited for age group, violence

The Bluest Eye by Toni Morrison

• Reasons: Offensive language, sexually explicit, unsuited to age group, violence

The Absolutely True Diary of a Part-Time Indian by Sherman Alexie

• Reasons: Drugs/alcohol/smoking, offensive language, racism, sexually explicit, unsuited to age group

Fifty Shades of Grey by EL James

• Reasons: Nudity, offensive language, religious viewpoint, sexually explicit, unsuited to age group

The Hunger Games by Suzanne Collins

• Reasons: Religious viewpoint, unsuited to age group

A Bad Boy Can Be Good for A Girl by Tanya Lee Stone

• Reasons: Drugs/alcohol/smoking, nudity, offensive language, sexually explicit

Looking for Alaska by John Green

• Reasons: Drugs/alcohol/smoking, sexually explicit, unsuited to age group

The Perks of Being a Wallflower by Stephen Chbosky

• Reasons: drugs/alcohol/smoking, homosexuality, sexually explicit, unsuited to age group

Bless Me, Ultima by Rudolfo Anaya

• Reasons: Occult/Satanism, offensive language, religious viewpoint, sexually explicit

Bone (series) by Jeff Smith

• Reasons: Political viewpoint, racism, violence