RESPONSE: These are great questions. And it is fair to ask for reasons that are biblically based. I will do my best. In that regard, I think a lot of people start in the wrong place with this discussion. I will come back to the passages that you referenced your question, but I prefer to start with a couple of passage that I think speak to any apparent "grey areas." By the way, In my response, I am going to use the term "extreme music" because I believe there are other styles that could be brought into the discussion.
Paul tells the Corinthians "All things are lawful for me, but not all things are profitable. All things are lawful for me, but I will not be mastered by anything" (1 Cor 6:12). Then he tells them again, "All things are lawful, but not all things are profitable. All things are lawful, but not all things edify. Let no one seek his own good, but that of his neighbor. Eat anything that is sold in the meat market without asking questions for conscience’ sake; for the earth is the Lord's, and all it contains" (1 Cor 10:23-26).
Of course, in the second verse, he is speaking specifically to dietary rules. But we shouldn't simply pass over that as if it only about food. This was a very serious Old Testament command that was being examined--no less than idolatry was in question. Furthermore, within the context of his letter to the Corinthians, Paul is generally addressing serious moral issues and liberties that Christians feel like they are able to take--issues which are causing serious harm. The city of Corinth was well known for it's wickedness. So Paul, having heard of the terrible things going on there, says what I have referenced above. And what is he saying? He is saying that whether or not something is forbidden is not the main issue (although certain things are clearly forbidden). He says, in effect, whatever you do, you have to ask yourself this: A) Is it wise? B) Does it build others up? C) Is it your master? D) Are you going against your conscience by doing it? If it is wise, builds others up, isn't your master, and doesn't go against your conscience, then go for it. Read the rest of the context in chapter 10 and you will see what I mean. And why does he say "go for it"? Because everything that exists belongs to God (vs 26), and if used properly--if brought into the service of God--is good.
Now, I hope you haven't gotten ahead of me, because you may be surprised by the conclusion I draw from that. Here's the thing: I believe that music is an incredibly powerful, and therefore dangerous, tool. Extreme music is doubly so. It can be used for great good but also for great evil. It stirs up people's hearts and emotions in a way that almost nothing else does.
Therefore, I think that Paul's "test" should be applied very carefully when it comes to music (as well as other forms of art/entertainment/media). It is not forbidden for Christians to play and/or listen to extreme forms of music. However, I am convinced that it is probably not wise for most Christians to do so. You heard me right. I think that probably more than 90% of Christians who are involved in playing and/or listening to extreme music (even if it is called Christian), are playing with fire.
So the question is: can something like heavy metal that sounds "worldly," "pagan," and "demonic" be used to glorify God? I absolutely believe it can. First and foremost because no one is able to create anything who does not ultimately get that creativity from God (the Earth is the Lord's and everything in it). As such, I believe that it is actually the satanic and pagan bands that have done the twisting--perverting something intrinsically good, that should be glorifying to God--rather than Christians trying to take something that is inherently evil and whitewash it to look Christian. But just to stick to what you requested, I will go back to Scripture and try to demonstrate what I mean.
We know that David visited the city of Gath, a pagan city, and discovered what was apparently a new stringed instrument, or a new style of music. He proceeded to compose Psalms 8, 81, and 84 for that instrument or in that style. Remember, Gath was a city of the Philistines, Israel's sworn enemies. It was in that context that David wrote these Psalms. Obviously, many churches would have rejected David and these songs for being "too worldly" or "sounding pagan." David effectively redeemed that musical instrument or style--using it to point to the one true God. The same has been done with many traditional hymns which were simply Christian lyrics set to popular melodies. Fanny Crosby loved to do that. One excellent example is the song "I'll Fly Away," which was written by Hank Williams.
Another biblical example of God redeeming a pagan practice, is the rite of circumcision. The Egyptians practiced circumcision before the time of Abraham. Even so, God chose to redeem the practice and even make it sign of the old covenant.
So, do I think that Christians ought to just go around looking for things that are sinful and trying to “redeem” them? What about illegal drugs? Should Christians be trying to find a way to redeem the use of heroine? Of course not. But Christians should be on the cutting edge of drug prevention and pharmaceutical advancements to help try to get people away from using chemicals that can be used for good, for evil. Should everyone become an undercover drug officer—working for months and years in terrible environments? No. Most people can’t handle that. Many would fall into the lifestyle in a very short amount of time. But some can, and they are incredibly necessary. I think the same applies to being involved in extreme forms of music.
There is also a problem of consistency for a person who would deem a particular musical style evil. I could just as easily argue that many of the beloved hymns of the last two centuries sound “dark,” “lustful,” “pagan,” and “worldly.” Why? Because they sounded exactly like the music that used to be associated in saloons, brothels, casinos. Just go to Youtube and listen to “Cowboy Saloon music” https://www.youtube.com/watch?v=JGTfyOiVQPA then follow it up by listening to “Gospel Song, I like that Old Time Religion” https://www.youtube.com/watch?v=A4GwTQj5msk. The first sound is traditionally linked to fornication, drunkenness, dishonesty, untimely death, gambling etc. The second is considered by many to be what “real Christian music” sounds like. But the musical style is exactly the same. Furthermore, I will personally testify that the sound of a pipe organ (which is common in many "traditional" church services) conjures up feelings within in me of death and darkness. Why? Because I associate that sound with funerals. But I am not going to tell my pastor that it is too “dark” and “gloomy,” simply because that is how I perceive it. Clearly, there are many in the church who absolutely love that sound. For them, it conjures up memories of revival time and/or when they gave their lives to Jesus. Nor am I going to write an email to Bill and Gloria Gaither and tell them that they are "false prophets" because they have led people to believe that this terrible saloon and brothel music is of the Lord when it is clearly not—that they have "tried to present peace where there is no peace" and as such, "God will lay waste to them" (all of the quoted lines are things that I was accused of during my time in a band). No. I understand that the style of music has been redeemed by God’s grace and has done powerful things in the lives of the last few generations. The creativity and beauty of making music has always belonged to God, and as such, cannot be destroyed no matter how associated with evil it may become.
Now, what about the issue of “not being friends with the world,” and “avoiding appearances of evil”? I would simply say that Jesus apparently failed at both of these IF we think that they mean we cannot do anything that the world does. He was/is a friend of sinners, and he was constantly getting accused of doing wrong. He was even accused of being a drunkard and a glutton (Matt 11:19). Shouldn’t He have just avoided wine and/or certain foods since He knew that people would think bad of Him for it? No. Because that isn’t the point. Going back to Paul’s "test", to be like the world, be friends with the world, or love the world, means to let the things of the flesh become our master. That is what is truly forbidden. It is not that we cannot do things that people in the world do. It isn’t even that we cannot look like the world. For goodness sake, Paul had Timothy—a grown man—circumcised, just for the purpose of helping him reach the Jews (don’t ask me how they went about verifying it) (Acts 16:3). And this is Paul, the same guy who says that if you are uncircumcised when you become a Christian, you shouldn’t get circumcised because to do so would be sin (1 Cor 7:18). Wait a second… isn’t that a contradiction? No, because with Timothy the purpose is to reach people for God. In the other case, people were being told by the Judaizers that unless they were circumcised (followed the Jewish laws) they could not really be saved. Huge difference.
In sum, I have no reason to think that any form of music is forbidden for Christians to make and/or listen to. However, I firmly believe music is very powerful, and therefore, inherently dangerous—especially to young people who are quick to define their lives by it. Extreme forms of music are doubly dangerous, especially when they are tied to a subculture (and they almost always are). For that reason, I think they should be approached very carefully. I would go further and argue that it is almost certainly not wise for the majority of believers to be involved in these styles of music. Even so, all forms of creativity are a gift from God and were intended to glorify Him. Thus, I believe that which has become associated with darkness can be redeemed. I hope that helps. Thanks for the great question!