I think motive is a very important issue to the life of a young Christian (indeed, any Christian), and the problem is that motive is so hard to discern. How hard I find to even discern my own true motives at times, and how deceptive the human heart can be!
What I mean by this, is that, if you're like me, settling for what's "good" until we can show them what's "best" doesn't feel great, even though it's all we can conclude sometimes. In fact, if you haven't heard it I'd encourage you to listen to Art Katz' sermon on 'The Good and The Perfect'. If we settle for good, maybe we're in danger of never attaining the true 'best' that we speak of.
This at least convinces me that if something is outright wrong, we should probably stand up against it, even if it risks alienating some of our youth. If it's something, like some of these festivals, with a bit of good and bad, it's really a bit more challenging.
My experience is that I could make my experience good or bad, which brings me back to motive. When I listened to Christian music that perhaps wasn't the best, my relationship with God was more shallow and my theology disturbingly incorrect, I was still sincere in my desire to follow after God. And HE brought me out of those things and into more maturity as time went on.
So my current thought is that if a young person is passionately seeking God, but has some things incorrect, to an extent (and within reason and wisdom) let them seek after Him in what might not be the best areas, because HE will guide them, I am sure of that.
"Ask and it will be given to you; seek and you will find; knock and the door will be opened to you. 8For everyone who asks receives; he who seeks finds; and to him who knocks, the door will be opened."
It may be that at some points he uses us to guide them. With some of my incorrect theology of the past, it took some people having an argument with me for me to see the wrong, but that took time.
The truth is, and my hope is, that when I look back on where I am now in 5 years, I'll be thinking "I was immature and incorrect compared to how I now know God", so I don't want to be too keen to try and force my walk onto others.
In practical terms, I think we have to trust God to guide us on a person by person basis. And also pray that we can end up like Paul and be able to say "imitate me, as I imitate Christ".