I agree with polarity about people's values, beliefs, etc, affecting what kind of music they listen to and play.
Personally, I come partially from a Christian background and I do believe God exists. I stay away from most black metal bands because of their ideologies and purpose. I listen to metal, but I don't believe metal is anti-christian at all. Some bands may be, but who said music is?
From my beliefs, attitudes toward life, and personality, I listen to the music I like. For example I listen to a lot of emotional, melodic, and depressing music such as Opeth, Pain Of Salvation, Nevermore. I am not depressed, but rather from the way I grew up, I can feel the music that way. From my attitudes in life, I feel the music I listen to and it pleases my ears. It's hard for me to listen to a band like Iron Maiden, because their music doesn't agree too well with my personality. It's too happy happy for me, as is most power metal.
The music I make will agree with my personality and views in life.
Now I don't care how you all see it, this is the way I see it. I'm not gonna state all this as Fact, but rather it's the way I view music. I think Opeth would change their music a little because of their beliefs, but even if I were a Christian I probably wouldn't make a happy happy christian album, but rather I would add messages about my beliefs, but I probably wouldn't force a christian message in every song. I'd be like a lot of other metal bands that have Christian members, who don't really talk about religion in their music.