That doesn't quite fit, does it? Hearing that, you'd expect the Luftwaffe to fly over and starting bombing the place, or something equally unpleasant to happen. If it didn't, the scene wouldn't make sense.
Picture another scene: a dungeon, dark and dank. Prisoners in rags, unwashed, unshaved. A storm rages outside, complete with thunder and lightning. The mood is depressed, hopeless, and despairing. And overlaid is this sound:
That doesn't quite fit, does it? Hearing that, you'd expect the storm to break, and the sunlight to penetrate the barred window of the prison, and the jailer to enter and announce that all the prisoners have been pardoned. If it didn't, something would seem... wrong.
I use these examples to illustrate a truth of which we're all aware: certain types of music fit certain moods and situations. I don't know enough about musicology, psychology, or physiology to explain why this is, but I trust you all can recognize it as a bare fact and can accept it as such. We can recognize pieces as "sad," "happy," even "sassy" or "demented." TV and movie producers make use of this to accentuate their visual products with the appropriate sounds. A romantic scene will have music in a major key, slower, sweeping; if it's supposed to be a bittersweet love scene, it might move into a minor key, but still light in tone. A death scene will probably be in a minor key, perhaps moving a little faster, a little heavier in tone. In the two examples given at the top, the scenes described would be much better illustrated by swapping pieces. As they are now, the music doesn't fit the situation.
George Harrison once wrote that music adds another dimension to the words of a song. It's important, then, that it adds the right sort of dimension so that we don't lose the initial shape or texture of what we had at first. If it adds the wrong dimension, it's like trying to taking a two-dimensional square and add a third dimension to turn it into a sphere--you lose the original "squareness."
Picture one more scene: the Holy Sacrifice of the Mass is taking place. The priest is leading the faithful to the Throne of Mercy and presenting the Father with the Sacrifice of Our Lord, that we may receive forgiveness for our sins, and that we may be renewed in our spiritual life by being fed with the true nourishment of the Body and Blood of Christ. Time and space are compressed, and we are brought to Calvary 2,000 years ago, and to the Heavenly Jerusalem at the end of days, all at the same time. This is an event of glory, splendor, solemnity, and reverence. So, I ask you, does this sound match?
Does this sound say "solemnity and reverence"?
The songs may or may not be aesthetically pleasing considered in themselves-- a debatable point, but not the one at hand. The words may (or may not) be loosely based on Scripture--also not the point at the moment. Just consider the event they are supposed to illustrate. Consider the moment they are to adorn. They don't match. The music doesn't fit the mood. Playing a song that sounds like it's from a Broadway musical during the Mass is like decorating your house with Christmas lights for the 4th of July.
The people who composed this music, and the people who play it at parishes, may very well be devout and holy servants who are simply trying to praise God with their musical abilities. I don't question their motives or their intentions. I do think their sensibilities are off. If this is what they think would properly illustrate the Mass, I have to wonder if they have a proper conception of what the Mass really is all about. If that's the case, I attribute no malice to them; most likely they've simply been ill-formed.
Music of this sort affects the Mass such that it makes it harder to perceive the Mass for what it is. Music that sounds like pop music makes the Mass feel like a form of entertainment instead of worship. Music that sounds banal makes the Mass seem commonplace, yawn-inducing. Music that's saccharine is giving our ears cotton candy instead of the real sonic sustenance that will nourish them.
I think a lot of people agree with these sentiments, consciously or unconsciously, and are voting with their voices, or rather protesting with their silence: they don't sing.
Attention music directors: there are loads and loads of hymns out there with uplifting words and beautiful music befitting the Sacred Liturgy. Please use them. Please play them. You might just find folks will sing along.