I dont listen to slipknot, but I do like the style of music. AND there is an alternative to this in the Christian world.
Linkin Park has songs that deal with the reality of the feelings people have whether or not they are leading a Christian lifestyle. I listen to Linkin Park because that is the genre of music I like. I have listented to their lyrics and by judging by that, it's not putting negative notations in my head. I find no fault at this point.
We have to understand that God can use a non-Christian band to bring someone to the understanding that feeling lost or under pressure or even about to give up in life is a hopeless way to live and there must be more out there. He did for me.
Linkin Park, Beach Boys, Beatles and Nickelback are the only "NON" christian bands that I can listen to, the rest I listen to nothing but Christian music. (We have an awesome Christian Rock station where I live) But that is my own conviction. We have to becareful and not put God in a box, however, we do have to get on a personal level with Jesus to know what is right or wrong for each of us.
Just as with all things in life we are commanded to judge something--everything by it's fruits.
Matthew 7:20 So by their fruit you will know them.
It's not about the genre of music, it's about what's in the song. Judge the song by it's lyrics. If they are negative and will cause you to stumble? I would suggest according to God's word to stay away from it.
Listening to music that will justify fighting someone or commit violent acts is definately wrong. It is wrong because of what influence it will have on a person.
Also, just to throw this out there,
Romans 16:17 Now I urge you, brothers, to watch out for those who create divisions and sinful enticements that oppose the teaching you have learned. Stay away from them,
Music is a very powerful thing. It can and DOES influence a person. Becareful out there. Keep a watchful eye not to be deceived.
