There has been vigorous public debate about Traditionis Custodes (TC), the papal decree that has restricted use of the older form of Mass.
I don’t want to pursue that debate here, but to ask a question of opponents of TC. They have described the decree as “harsh”, “cruel”, and “severe”. Many of TC’s critics say that it removes the generosity toward lovers of the older Mass that Pope Benedict XVI extended in Summorum Pontificum and Universae Ecclesiae. They see Traditionis Custodes as curtailing a healthy liturgical pluralism.
Now suppose that the next pope is a strong adherent of the old rite; early in his pontificate he reverses TC, mandates universal use of the old rite, and places severe limits on or even abrogates “the liturgical books promulgated by Saint Paul VI and Saint John Paul II” (TC Art. 1). Not long afterward, he cancels all of the liturgical changes made since 1900.
Further suppose that a group of the clerical and lay faithful who love the liturgy of Paul VI come forward and ask the new pope to make generous provision for the use of the reformed liturgy, including in parishes. What would today’s strongest critics of Traditionis Custodes advise the new pope? Should the reformed liturgy be banned? Or would pluralism prevail here as well?
Many opponents of TC say not only that the older Mass should be preserved but that the Mass of Paul VI and its related content is impoverished, inadequate, assembled on the basis of bad scholarship, and otherwise defective. Peter Kwasniewski has written that the 20th century reforms to the liturgy were, at their worst, a sin against the Holy Spirit.  If this were so, why would the Church not restrict or entirely inhibit the reformed liturgy? Error, after all, has no rights.
There is a parallel to another debate around Vatican II, on religious liberty. John Courtney Murray SJ wrote this about Dignitatis Humanae, the 1956 Declaration on Religious Freedom:
A longstanding ambiguity had finally been cleared up. The Church does not deal with the secular order in terms of a double standard—freedom for the Church when Catholics are in the minority, privilege for the Church and intolerance for others when Catholics are a majority. 
So, the question to opponents of Traditionis Custodes: if the shoe were on the other foot, if the older liturgy were normative, how would you respond to calls for pluralism?
 See, among other examples, his lecture “Beyond ‘Smells and Bells’: Why We Need the Objective Content of the Usus Antiquior”
 “Religious Freedom,” in Abbott, ed., Documents of Vatican II, p. 673.