Why are the Afghans so upset about a loony in the US burning the Koran?

I just can't see what they are so upset about or why the US pastor was so intent on stirring things up. What is the matter with these people? Its just a book. Burning it doesn't make it more or less true and it serves not useful purpose either. The Bible and the Koran seems to make people sick in the head. I think we'd be much better of with a church based on the works of Monty Python. At least nobody would take it too seriously. Or would they?