Funny that I should see this topic, it's been something that God has brought to my attention lately.
I have five guy friends who are not allowed to listen to rap. They're all growing up in wonderful Christian homes, and I know that their parents are only aiming for what is best in God's eyes for them. However, I personally love Christian rap, so I've been trying to understand more where they're coming from.
I think music can definitely influence our behaviour, especially if we don't watch ourselves and put the sound above the lyrics. Obviously, these boys' parents know them much better than I do. I'm sure they know the conditions of their boys' hearts and what could tempt them and cause a longing for non-Christian music, or cause ungodly attitudes. Especially in today's world, the contemporary rap culture is NOT very promotive of a Christian lifestyle or encouraging for a young Christian guy trying to fight against temptation. For me, listening to KJ-52, Grits, Cross Movement, Toby Mac, etc. does not give me a desire for Eminem, 50 Cent, etc. because I'm looking for something deeper than just sound - I'm looking for something that builds me up in the Lord, something that mixes a cool beat with the "coolest" Story ever told.
So it's about being filled and built up for me. But I also want to be sure to watch myself as well, to make sure that I don't allow the SOUND of the music to become an idol to me over the lyrics, which point to God. Utlimately, I think everyone's different, and it's a personal decision as to whether or not you would be lifted or brought down by rap/rock.
It's the attitude of the heart that truly matters.