"Legitimate" diversity in the Church means that the Tridentine Mass is more widely available, that neither Opus Dei nor the Catholic Charismatic Renewal are the subject of defamation and slander, that an officially authorized variety of musical instruments and styles competently used and focused on praising God are respected, that self-crowned mini-popes don't go around vehemently imposing their personal opinions on clueless lay people as if such personal opinions are dogmas or definitive teachings of the Church, and that evangelists are free to reach out through legitimate inculturation to different ethnicities and cultures, whether they are historically Catholic or not. There are many other marks of legitimate diversity in the Church precisely because one of the four marks of the Church is her universality. As Vatican II said, she is the sacrament of unity for all mankind (Lumen Gentium, 1), proclaiming Jesus Christ as the one and only Lord for the entire world in all its diversity.
But then there are those who out of ignorance or fear or even something akin to an obsessive compulsive disorder of some sort insist on attacking anything that diverges from their own habits or customs. Sometimes I think even jealousy is involved as when the Pharisees despaired at the growing popularity of Jesus (see John 11:45-53). Sometimes some people attack precisely that which they desperately want or need because they cannot bring themselves to the humilty and abandonment to God that admits that they are indeed needy and that someone else may have gotten it first outside their own customary ways.
In Fr. Francis Fernandez's excellent series Conversation with God (Vol. 3) published by Scepter Press, we have commentary on this very same problem--the lack of tolerance for legitimate diversity in the Church. He begins by noting the famous incident in which Jesus turns back the complaint of the apostles that someone else was casting out demons in Jesus' name: "Do not forbid him; for no one who does a mighty work in my name will be able soon after to speak evil of me. For he that is not against us is for us" (Mark 9:39-40; RSV). Here are some of Fr. Fernandez's comments (he is a priest of Opus Dei):
1. "Christ . . . condemns a narrow-minded and exclusive attitude toward apostolate. He teaches us that the apostolic work done in his name can take many different forms" (p. 373);
2. "Our Christian spirit should lead us to be open to the most varied forms of apostolate to make an effort to understand them all--no matter how different they may be from our own way of thinking or of acting--to rejoice in their variety. . . . Rejoice when you see others working in a good apostolate. And ask God to grant them abundant grace and correspondence to that grace. Then, you, on your way. Convince yourself that, for you--yours is the only way" (p. 374; the originally italicized words quoted from St. Josemaria Escriva's The Way, 965).
3. Fr. Fernandez quotes the famous aphorism of St. Augustine as highly relevant to tolerating legitimate diversity in the Church: " ' in necessariis unitas, in dubiis libertas, in omnibus caritas' --unity in all that is necessary, freedom in all that is subject to opinion, and charity in everything' " (p. 374; original italics). The St. Augustine quote is taken from a speech given on October 31, 1982, by John Paul the Great in Spain to the Spanish Episcopal Conference.
4. "The Apostles and their successors made sure that, in all necessary matters, unity might be maintained. But the Church did not try to impose a straightjacket of uniformity on all its converts" (pp. 375-76; emphasis added by me);
5. Finally, especially for a Catholic like me who is involved in the Catholic Charismatic Renewal, these words of St. Josemaria hit home: "The wonder of Pentecost is the sanctification of every unique path: no one way has a monopoly, no one way is to be encouraged to the exclusion or the detriment of others. Pentecost is an incalculable variety of tongues, of methods, of ways of meeting God, and not a forced uniformity" (p. 375, quoting Furrow, 226; original italics).
Of course, the toleration for legitimate diversity applies to me as well. That is why I root for greater tolerance for the Tridentine Mass, although I do not regularly attend one. That is why those who do love the Tridentine Mass should rejoice in the renewal and the vocations fostered by the Catholic Charismatic Renewal and other apostolates in the Church. That's why in my own personal experience, I have respectfully (and hopefully charitably) confronted, when prudent and necessary, both "liberal" and "traditional" Catholics who have tried to impose a "straightjacket of uniformity" on orthodox, loyal Catholics following the magisterium in the great Catholic Church of all ages and cultures.