I think we need to make a distinction between sacred music for use in church and music produced by Christians for Christians (or a general audience even).
There are musicians and bands who are Christians and produce music I enjoy because I find it aesthetically pleasing and interesting, but would never want it as part of the Divine Service as it simply doesn't belong there.
The Christian produced music I do enjoy I enjoy for many of the same reasons I enjoy "secular" music--because it is aesthetically pleasing and interesting. Not because it is "Christian".
I also hold sacred music to a much higher standard to, let's call it "listening music", based on the principle of Lex Orandi, Lex Credendi--the law of prayer is the law of belief. Sacred music serves a deep theological purpose in the Service as part of the overall Christian
leitourgia, what we are doing together as God's people assembled to receive God's Word and Sacrament.
A major flaw occurs when we start to think that "Christian music" is somehow a kind of holy substitute for "normal music" and that we are supposed to be in some kind of weird cloistered subculture with our Christian-branded music, clothes, and various paraphernalia.
So to that end do I have a problem with rock music produced by Christians? Of course not. But then I like various kinds of rock music, among many other musical genres.
But I don't think it has any more place as use as sacred music in church than I do "secular" popular styles of music.
Having said that I don't have a problem with Christian-produced rock music--in principle--I do think there are plenty of valid criticisms to be had about CCM and its industry as a whole, and with the kind of ethos is promotes; e.g. the cloistered "Christian" subculture I mentioned above. I also think other valid criticisms are that frequently the music simply isn't that good, and the substance can also be deeply lacking if not just plain bad--
especially if used theologically. But that's something that needs to be critiqued and analyzed on a case-by-case basis. I think the sharpest points of this critique go to so-called "praise and worship" music, which tends to be theologically shallow, emotionally manipulative, and driven by consumerist tendencies, but billed as sacred music anyway.
-CryptoLutheran