I read a question from a Catholic in the Roman Rite recently asking what was wrong with adding whatever musical instruments people like to the music during the Mass. The underlying intuitions here are that the Mass can be customized to suit our likes and dislikes, and that our likes and dislikes are the deciding factor in how the Mass ought to be celebrated. These are understandable intuitions in a culture in which mass media constantly inundates them with messages about how this product, that product, and all of life should be tailored to their whims so as to get them to buy their products. These are understandable intuitions for people who have become so accustomed to being entertained by musicians, comedians, movies, and television. There is understandably a deep intuition rooted in popular culture that people on a stage ought to be facing them as a means of inviting them to participate, and it's no surprise that they would find it hard to break that habit when they attend Mass.
But the deeper problem is that they have come to see the divine liturgy as a thing in that category of things which are products for our consumption. As has been pointed out very eloquently at the BadCatholic blog, the liturgy is supposed to be different from the ordinary experiences of our lives. It should draw us out of our own likes and dislikes and into divine love by creating a sacred space in which we can build a habit of separating ourselves from the world long enough to renew our relationship with the divine and strengthen ourselves for going back into the world and bringing that divine light with us through our experiences of God in the liturgy.
This does not mean that we cannot have likes and dislikes, but it does mean that in the liturgy we are not there to ratify our likes and dislikes, but to reshape ourselves in the image of God. Much as we might allow our friends and family to choose what food we will eat for dinner when celebrating their birthday, we allow the Church as the bride of Christ to choose how we will celebrate His sacrifice on the cross, the sacrifice made so that we might exist in eternal union with the divine.
This sacrifice is eternal and our celebration of it should be no less so; it should not be a product of our whims or tastes so much as a participation in the forms which connect us with the Apostles, the early Church, the medieval Church, and the Church which still exists in our own time in unity with the Church throughout history and into the future. The liturgy is not ours to do with as we wish; it belongs to the Church eternal and not exclusively to the Church of one generation. We are stewards of the liturgy which existed long before we did and are charged with preserving it for future generations.
There is nothing wrong with the liturgy changing in form so long as those changes retain the underlying structure and theology which keeps us connected to the Church eternal, but there is a great deal wrong with changing the forms of the liturgy with a complete disregard for the Church of the past and the Church of the future because we are fixated on arranging things to our taste. If I were to advocate my own tastes as rubrics for the Mass, then I would have European melodic metal playing, but I recognize that my tastes are not the deciding factor in how the liturgy is celebrated. Nor should they be.
The liturgy is not a product created for our convenience like so much else in our lives, and we should not treat it as if it were such a product. The liturgy is a profound and timeless celebration of the sacrifice on the cross which allows us to grow in union with the divine by pulling us out of our world of self-centered convenience and into the world of loving sacrifice lived for all those loved by Christ.