Metal is a misunderstood genre of music. This was the philosophy that was first given to me when I began to listen to it, and it has certainly stuck. Metal is perceived by many as a bunch of oddly dressed idiots screaming into microphones about Satan while being backed by noisy guitars. Don't get me wrong, there are several bands that do that. But that is not what metal necesarily is.
Metal discusses a very broad range of topics, from the macabre of death and suicide, to the dorky slaying of dragons and mystic kingdoms, and the rock-and-roll classic theme of untrue women. Oh yes, there is killing Christians, worshipping the Devil, and killing in the name of the Norse gods as well. The particularly angry and angsty tone of the music has been adopted by people who espouse such ideas. It is important to bear in mind, though, that most metal is not like this.