There were evil fae in old legends. Lots of them. And even the good ones weren't exactly 'nice.' There were more stories of Fae cursing and killing people than just about anything else. There are precious few old folkloric stories about the Fae being benevolent.
Also, the original Elves were a Norse invention, as were Dwarves. There were light elves and dark elves, and I don't know a whole lot about them, but I know that at least the Dark Elves were evil.
The elfs where often evil, and tricky characters. Here in north, Sweden they are called Älvor, and they where beautiful and lured in people with thier beauty, to kill them, or often trick them into falling into water to drown or off a cliff. Also they destroyed livestock and stuff like that. So Elfs where very evil here in Sweden atleast. And Elfs where made up here in the north I think. Elfs and Trolls are the most common creatures here, Trolls would switch a human child with a trollchild, and steal all gold they can come over. Man I need to look into some Swedish mythicalbooks again, alot of nice evil stories to read!