The late great singer-songwriter Jim Croce wrote a song called It Doesn't Have to Be that Way, which was included in his album Life and Times, the album that included the hit Bad, Bad Leroy Brown. Though not a Christmas song, It Doesn't Have to Be that Way gets a lot of airplay on mainstream radio during Advent.
I see so many things in mainstream Catholic liturgy that, as the title says, don't have to be that way. Here is a list of such things. These are either things I see, or things I may do that get sometimes questioned, usually by laity.
* The Responsorial Psalm doesn't have to be sung solo. It can very effectively be sung by a choir, or semichorus. Some of the best Psalm settings are sung in alternation, between a solo voice and choir, in which the solo voice chants a Gregorian tone (e.g., Psalm Tone 8G), followed by the choir (or semichorus) chanting a polyphonic tone. We do this sometimes at Sacred Heart with settings I wrote, and those of Sam Schmitt (see the Chabanel Psalms at Corpus Christi Watershed). Maestro extraordinaire Dr. Peter Latona composed a number of settings in the same way.
* The cantor doesn't have to blare into a microphone every time there is something to sing. I'm referring to those pieces of music belonging to the congregation (responses, propers, ordinaries, hymns). Let them sing. And, for cripes sake, if you have an able choir, you definitely do not need a cantor to blare into the mic so as to leave the choir in the dust. It just doesn't have to (and shouldn't) be that way.
* The entrance hymn doesn't have to be about us coming into church and "being one" with each other, thus the so-called "gathering song". I cannot stress enough that there is no such thing as a "gathering song". If you're singing while you're gathering, you're probably late for Mass. And if the song you're singing at that point really is about your "gathering", you're singing for the wrong reason. I don't know of one Introit (the true "entrance song" of the Mass) that focuses on gathering. If you can find one in the Graduale Romanum or the Liber Usualis, please let me know. Gather Us In and All Are Welcome do not cut it.
* Same goes for Communion hymn. The Communion hymn does not have to (and should not) be about us lining up for "a meal" and "being one". Wrong focus. We should venerate and adore who we are receiving, not ourselves receiving Him. I've gotten flack on message boards over the years saying that hymns like Ave Verum and Adoro Te Devote have no place in the Sunday Mass. But in all actuality, they have all sorts of place at Mass. Song of the Body of Christ and Table of Plenty do not. We can also do without One Bread, One Body, again, us-centered, instead of Christ-centered. At That First Eucharist (aka, Lord, Who at Thy First Eucharist) is a viable alternative.
* More on the Communion hymn: the music sung at Communion does not have to be "contemporary". I've been to Masses that often will use traditional forms of hymnody (chant and metrical), but, for Communion, resort to something that got its roots in Glory and Praise or Gather. Last I remember, the Communion proper from the Graduale or Liber wasn't meant to sound like a love ballad, show tune, or commercial jingle. Wait till after Mass and pop a CD in your car if you want that stuff.
* During Advent and Lent, in which less organ (or sometimes no organ at all) is prescribed, one does not have to resort to the piano. Yes, I've witnessed organists shift to the piano just because it's Advent or Lent. It's still instrumentation. Wheel that piano into the parish hall where it belongs! Use something off your usual organ registrations for that time, if need be, or even go a capella.
There will be more as they come to mind.
Quod scripsi, scripsi!