You can always quote a few lines without asking permission, but that's likely to be the same few lines that have become cliched with repetition. Quote the whole speech to make a more substantial point, and you face thousand-dollar license fee claims from the estate. Quote them to make a point critical of King, and you may be denied a license entirely.Link
I write books. My latest is a YA science fiction novel called Homeland (it's the sequel to Little Brother). More books: Rapture of the Nerds (a novel, with Charlie Stross); With a Little Help (short stories); and The Great Big Beautiful Tomorrow (novella and nonfic). I speak all over the place and I tweet and tumble, too.