Graphic novels are part of the wildly diverse, wacky, and rich gumbo of our culture. If you were teaching a history class today on the Holocaust in Europe, you would mobilize memoir (Ann Frank, Elie Wiesel) essay (Hannah Arendt, Thodor Adorno), and film (Shoah, The Sorrow and the Pity) to help students get a deep and meaningful, nuanced and complex picture of the entire sweep of the times and events. To leave out Maus would be to banish a fresh and intimate work that adds immeasurably to our overall understanding of the Holocaust.
Dykes to Watch out For is an essential text if you hope to understand the Clinton/Bush years. On and on and on: teachers integrate poetry and literature, art and science, film and painting into everything they teach.
Why not comics?
I teach a writing class on memoir, and I use Maus, Persepolis, Fun Home, and Epileptic along with Homage to Catalonia and Black Boy. Students respond variously, but I would be irresponsibly narrowing their horizons if I left out the comic books.