Oooooh! This topic is tasty! It's also, unfortunately, quite indisputable. You really have to weigh both sides without bias to fully grasp it.
On the one hand: Metal. Its earliest roots trace back to the Southern State blues of the early 1900s which was the music of the oppressed and enslaved, a way to let out their woes and come together in grievance and frustration. It was in no way uplifting or immaculate and there, of course, exist the rumours of those who even sold their souls to "the devil" in exchange for blues fame and talent. From the blues came rock and from rock came metal and throughout the progression the music became increasingly loud, aggressive and "sinful", promoting the ideas of sex, drugs and alcohol. Even musically, the use of the tritone or "the devil's chord" (a diminished fifth) was heavily frowned on by religious traditions. It is perfectly understandable, especially in the West, why anyone would consider the amalgamation of metal into "Christian" culture hypocritical.
On the other hand: "Christianity". Literally, the ianity of Christ. Those who believe in Christ and strive to follow his teachings often call themselves Christians. Unfortunately for you, rice, there is no definitive "Christian" church. The title is left solely to the individual, regardless of what religious sect they follow, and it is up to them to determine just how "Christian" they are. It has always been the organization that has been the oppressor and the censurer of music, race and culture, for which I'm sure most anti-religious people detest them. I was raised a Mormon myself (and almost went on a damn mission too!) and I remember my mother shouting at me for "listening to that crap!" upon finding an ACDC album a friend had lent me. However, I never heard anything against such music otherwise from any teachers or missionaries in that particular sect. Though here are a few interesting links to read up on:
http://www.lds.net/forums/276341-post8.html
http://www.metal-archives.com/board/viewtopic.php?p=715238#715238
Personally, I'm into metal because of the talent it requires and the energy with which it's played, and I can sympathize with someone who would like to enjoy those same qualities in their music without having to listen to someone viciously attacking their close-held beliefs. Retrospectively, it is pretty wrong to see a group of people saying, "Hey! This stuff ain't so bad after all!" It's like a kid learning to appreciate broccoli after years of rejection and you just want to smack him on the forehead and go, "NO DUH!" but really, in a global sense where some people are actually just trying to get along I don't see why we can't all just unite under metal.
\m/