"Jesus said; 'you are either for me or against me.'"
REALLY!?!? I think you're thinking of George W. Bush. And you have no authority to compel adherence to this or that sect, dogma, or path. He calls many, and each in their own way.
If he truly loves the Lord he will get away from secular music and invest a lot of quality time studying the word and praying and being with people who can help him get a clean break from all that is ungodly and unholy.
He can't have one foot in the world and the other in the kingdom. Jesus said; "you are either for me or against me." He can't have it both ways.
The Lord calls us to separate from this world and live for his glory, honor and praise. Anything less than that is smoke and mirrors.
IN this world, Not OF it. That's different from the Cult of Death you're describing.