One of Terry Jones' convictions is that the Koran is evil. Really. He's not a mainstream kind of guy. As an expression of his religion (again, whether you agree with it or not), he wanted to burn the book he thought was evil. There's plenty of precedent.
Book burnings are not rare. Why do we only find this one offensive?
We arent talking about the latest dan brown book here, we are talking about holy scripture, there is a big and quite significant difference. My objection to this is that religion is not violent, true people of faith regardless of their religion only ever talk about tolerance towards others. I know many christians, muslims, sikhs and hindu's and none of them would ever talk about another faith as being evil, merely uninformed.