If they're there, you may as well entertain them. In fact, you have an obligation to entertain them, so they don't sin by not showing up. They may be showing up to be entertained, but that doesn't matter, because at least they won't go to Hell. Mass is filled with people who hate church and don't want to be there, and the music reflects that.
Making an excruciatingly learned decision about the degree of sin or disobedience invloved in deciding whether or not to participate in musical drivel, or endure the un-holy noise of rock bands? This is pure, Jesuitical legalism... which one should be presented with no occasion to entertain at mass. (Indeed, I should think that any burden of sin rested, rather, on those who present such dilemmas.)
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