I feel it is important that I make some sort of effort to comment on the misconception that heavy metal and Satan are walking hand in hand. While it is blatantly obvious that Satanism has been fused into many lifestyles of heavy metal lovers, to say that heavy metal is of Satan is ludicris.
The first problem with this stereotype is the fact that many people are not acknowledging that Satan is merely a symbol in the work of many bands. There are very few bands that come to my mind who actually express theological Satanic beliefs (classic black metal band Mayhem comes to my mind, and even this is somewhat questionable).
The second problem is that music is a means of expression, in all aspects: religious and non-religious. My biggest qualm with the "hate" of Satanic music (and moreover, heavy metal as a genre) is how easily accepted genres of music such as Christian rock, Worship music, and such are. Why is it okay to listen to bands sing about Jesus Christ and God, yet not symbolically (or theologically, for all I care) Satan? It seems to me that religion is really dictating what is "okay" to listen to, but in such a way that is downright ignorant of other viewpoints.
One may be tempted to say that the subject matter is what makes the difference. Songs of Christ heavily dictate a loving and hope-filled atmosphere, whereas many Satanic songs are depressing and violent. While in some respects this may be the truth, music undeniably drives people towards specific sensations and emotions. Music is visceral. Conscious human emotion is a peculiar thing, and music is merely a method of expressing emotions; whether they be dark and depression or light and happy. Additionally, we may consider Satan the great destroyer and bringer of darkness; however as we analyze musical themes, let us not forget the many dark qualities found within various religious movements. I am led to the occasional heavy metal band whom tackle the religious crusades. My mind gently drifts towards Iron Maiden's "For the Greater Good of God" as it relates heavily to this subject matter. This is even more important as far to frequently Iron Maiden is deemed a "Satan worshipping" band, though this is not evident in any of their songs if you actually examine them.
I know that some metal bands push it a little far with their anti-religious sentiments, however when one considers how much damage religion has caused over the ages, it is fairly understandable to see why these people are in a rage. I do not intend for this article to be much of a religious discussion, but rather one where hopefully individuals will open their minds and not judge every artist who plays loud music without examining the facts of their art.
NOTE: The image seen to the above is that of Gaahl of black metal band Gorgoroth. One interesting aspect of Satanism is the usage of theatrics to get across a message. Black metal (a discussion in and of itself) artists have the tendency to dress up in very dark, atmospheric costumes and apply "corpse paint" to their bodies to give the appearance of the death. Except for a few individuals, this is purely an act to which many people gather around (especially angsty teens). Some will certainly not agree with it, but it is interesting to understand why bands do this (especially Satanically speaking).