External participation is praised, as well as those who facilitate it:
105. Therefore, they are to be praised who, with the idea of getting the Christian people to take part more easily and more fruitfully in the Mass, strive to make them familiar with the “Roman Missal,” so that the faithful, united with the priest, may pray together in the very words and sentiments of the Church. They also are to be commended who strive to make the liturgy even in an external way a sacred act in which all who are present may share. This can be done in more than one way, when, for instance, the whole congregation, in accordance with the rules of the liturgy, either answer the priest in an orderly and fitting manner, or sing hymns suitable to the different parts of the Mass, or do both, or finally in high Masses when they answer the prayers of the minister of Jesus Christ and also sing the liturgical chant.
An interesting distinction is given between low Mass and high Mass, wouldn’t you say? First, participation in either form is praised, spoken and sung. Second, what do you think about the presumption of hymn-singing at Low Mass, and singing chant at high? If singing hymnody and contemporary liturgical songs caught on after the Council, with full approval of bishops and pastors, it would seem the thinking was that we were just retaining low Masses, just with more flexibility in terms of what could be done. And perhaps, for many communities, the High Mass was just altogether out the door. A liturgical “movement,” rather than a statement (necessarily) about musical style? What could have been done to avoid that? And would church musicians have been on board with the effort?