We shouldn't judge people for things such as what they eat, what day(s) they worship, what time they get up in the morning ect... Not everything is "not to be judged." We are not to blindly walk around oblivious to people and our surroundings. We should surely use our judgment in situations. God gives us discernment for a reason. If Skillet started throwing up the middle finger would you feel the same way about them?
1 Tim. 5:20,
2 Tim. 2:16-17,
2 Tim. 4:14-15
I don't like Skillet for reasons that are my own, but if I'm going to listen to a christian band and they were to so boldly make a statement such as throwing up their middle finger, no, I wouldn't support them. But what makes them more likely to do this than a worship singer?
Mike Guglielmucci was a worship leader with Hillsong United who faked cancer going so far as to preform with an oxygen tank in order to take money from people to fund his underground pornographic film company. CCM singers Sandi Patty and Michael English were both caught cheating on their spouses. Raze was a short lived CCM band that disbanded after one EP because one of their singers was arrested for raping under age girls.
In all my years of listening to christian rock/hard rock/metal and whatever "evil" genre, I have yet to hear about those bands doing such things. I know they're not perfect. I'm sure they make mistakes, we all do. These people aren't perfect and we can't expect them to be. But to think they're more likely to be evil by playing "worldly music" (which is no more worldly than watching tv's or wearing jeans mind you) is ignorant.
Of course God says not to love the things and practices of the world. Number one, God should be our first love anyway, and number two, people that are of this world can draw us away from His love if we're not careful. That verse is about choosing the things of this world over God. I have no conviction about what I listen to, and it helps strengthen my faith and belief.