Much of the Christian" or "white" metal is just as demonic as the black metal, so make sure you know what you listen to
I do however not think that the music in itself is good or evil, the meaning behind it is. - Usually reflected in the lyrics...
When I feel down, far from God, or angry, the calm music will ususally just make me more upset, because a lot of it is too happy. Then I need someone singing about how life is miserable for a while, before i can go on to the happy stuff.
Look at the lyrics, and look at what then band represents (ex in their CD covers). Thats what matters, not if they scream or not.
The Prodigal son - Extol:
Why did I leave?
Lost, fooled, confused
Crawling in the mud with pigs
Starved to death
Discouragement strangeling me
I have no breath
Full of sorrow and despair
The father lets his son away
Challenging the world without fear
Unknown of the evil atmosphere
Imperfect man, imprudent mind
Disobediant to the call of God
Exhaustion becomes perdominant
Hell on earth is where I am
I'm longing back to a life in peace
With abundance of food
And plenty of water
I'll return to my father's house
And tell him I'm worthless as his son
Father please forgive me
For I have sinned against you
Regretting man, independant mind
Attraction to the call of God
With open arms the father
Welcomes his son back
He was dead and became alive
He was lost and has been found
Spiritual satisfaction
Inner peace
Comes from the Father