In 1966, a former Conciliar peritus, Fr Ratzinger, wrote some very far-sighted words about Ecumenism: "The Catholic has to recognise that his own Church is not yet prepared to accept the phenomenon of multiplicity in unity; he must orient himself towards this reality ... the Catholic Church has no right to absorb the other Churches. The Church has not yet prepared for them a place of their own, but this they are legitimately entitled to ..."
It is important to realise that this idea, of preparing a place for separated ecclesial bodies, does not exclude an 'Ecclesiology of Return'. Those who have wandered from the Unity of S Peter need to return, and return must imply a full acceptance of everything that the the Catholic Church has dogmatically defined as to be accepted as of Divine Faith: everything defined both before and after the original separations. But that being said, the Church should indeed 'prepare places' in which those who have been separated can flourish with their own charisms.
Anybody who denies this is denying the propriety of the processes employed by the Holy See for many centuries in welcoming 'uniate' communities.
But, even when it is a matter of the re-integration of groups within the family of Western Catholic Christianity, there has been the problem of the differences between these groups and the ethos of what we might call the 'mainstream' Latin Church. Just as the Popes, for centuries, had needed to work and to legislate and to exhort in order to prevent the Eastern Catholic sui iuris Churches from being 'Latinised', so there remains a persistent tendency for the 'mainstream' of the post-Conciliar Western Church to be uneasy about the very existence in its midst of groups which are different from the Novus Ordo ethos which has taken over much of the Western Church.
In theory, especially among 'liberals', diversity is a trendy in-thing. In reality, among management circles generally within the Latin Church, diversity is about as truly popular as a Rumanian Beggar at a Mayfair Wedding. There are those who have a deep visceral suspicion of any others whose expression of Catholicism is at all different from their own. Readers will remember the uproar among 'liberal' prelates, the Trautmanns and the Wuerls and the Murphy O'Connors, about Summorum Pontificum. Someone should put together a jolly little anthology of the various 'guidelines' dreamed up by some such gentry in order to impede and evade the plain meaning of that piece of papal legislation.
'Tolerance' is fine as a mantra as long as it doesn't dare to take itself seriously.
I can think of three example: the FSSP, the FFI, and the Ordinariates.
To be continued.