There's a large section of the underground metal scene that takes a rather principled stance against Christian music, and one that I've never fully understood. Viewing Christianity as a poisonous ideology? Fine, all well and good (though expressed more adolescently that I'd like it to), but refusing to listen to Christian music due to its inherent Christianity? Well, the silliness of this seems obvious- whether you necessarily know it or not, you likely listen to musical artists with differing (or even abhorrent) ideologies all the time, and taking a stance against Christianity specifically is a positional move. Not to mention where exactly the line falls with what defines something as "Christian" band. There's numerous musical collectives out there which feature Christian members (many of my own musical projects included) where Christianity is not actually a feature of the music. If there's anything my experience has taught me, it's that Christians are just as able to write songs about shit-eating serial murderers as the staunchest atheist.
However, there's the obvious trouble of Christian bands proper- where Christianity is an inherent ideology to the music that is expressed lyrically and musically. My issue with them has nothing to do with the ideology- I regularly listen to anti-white hip-hop with little concern, as I'm an adult who doesn't get virulently offended by those who might be positioned against me. Art is art. However, I have to speak out the other side of my mouth here by saying that most Christian metal (and Christian music in general) is quite terrible. I have a number of Christian bands in my personal musical collection, but only a small handful that I would listen to any regularity- those that, on a musical level, can stand up to their secular counterparts. It seems as though the best Christian metal is usually tied to hardcore or metalcore; Impending Doom, Common Yet Forbidden, and (to some degree, I suppose) Killers By Trade are all worthwhile artists in their particular fields.
So why does Christian metal usually fall flat on its face? Well, it's a simple matter, and very similar to the reason that NSBM fails so often: because it places ideology before music in many circumstances. If you would like to preach the teachings of Christ or a stance against some nebulous Zionist conspiracy, that's all well and good (though I think the positions themselves might be silly), but be sure to have sick riffs as well. Most Christian and NSBM bands do not because there's no system of quality control beyond expressing an ideology. Labels like Open Grave Records and any number of CDr NSBM labels often release very substandard releases that are only given a proper release due to their agreement with a label's particular ideology- the sheer number of terrible, terrible NSBM releases I own expresses this very clearly. Beyond the inherent litmus test of ideology, such labels seem relatively unconcerned with musical quality despite how substandard it might be.
But to divorce Christian metal from the NSBM comparison for a moment, I'd say that there's a deeper issue with Christian metal which prevents so much of it from being musically feasible which is, in part, tied to ideology. I don't inherently believe that the expression of Christian values is naturally antithetical to metal's basic aesthetic and conceptual tropes. However, the way many Christian bands go about it continues to drag them down to a feeble, uninteresting level. Christian bands, in effect, preach to the choir: ideologues simply looking for a reiteration of their personal values without any concern of fitting in to the genre they're ostensibly a part of.
Christian music (Christian metal included) comes from a position of conversion and propaganda more often than not. The goal of a Christian band is rarely to simply create great art where the ideology happens to be a part of it; rather, the priorities are switched. To be more precise: Christian metal tends to come from a position of weakness rather than strength. This is partly due to the form of Christianity preached in such music. Rather than taking the old testament's position on power, glory, and aggression against unbelievers, Christian bands tend to adhere to a modern, liberalized brand of Christianity where inclusion and egalitarianism is more important than the values of the religion itself. Christian metal is badly in need of a massive revamp to be relevant.
Anyone even loosely familiar with Christianity is fully aware that the Bible contains numerous tales of extreme subject matter perfectly fitting the aesthetics of metal: the suffering of unbelievers in hell, God's wrath striking down the unworthy through devastating displays of natural power, and an acceptance of suffering and cruelty in order to achieve a greater goal. So why is it that the lyrics and music of Christian bands don't convey this sort of awe-inspiring force of will and terror that the Bible so clearly emphasizes? Well, it's quite simple: people aren't as easily converted by tales of brutality and extremity as they are promises of the gifts of heaven. Yahweh, as we know, was quite cruel in the olden days of the religion, cursing those beneath him who did not properly worship- in short, extremely metal and viable as a topic for metal music.
So what is my ideal metal band? A group of fundamentalist, old testament Christians who are less concerned with converting unbelievers than damning them. I would love to see a Christian band that reveled in the suffering of heretics, telling stories of the destruction of entire city's through god's punishing hands. I don't need to be preached to- hell, a metal audience would likely be more interested and receptive to the ideas of Christianity if they were presented from a position of dogmatic, inexorable strength rather than the weak-kneed tolerance of modern Christianity. Long, dirgelike funeral doom songs detailing the suffering of Christ during the passions, violent black/death songs describing the smashing of Egyptian armies by the violent, swirling tides of the Red Sea- these are the stories and ideas I want expressed in metal, not a pitiable request that you repent, you know, if you feel like it.
Christianity can be metal. It's unfortunate that so many Christian metal bands reject it.