There are many who believe that the politically correct concept of "diversity" is something that makes life better for everyone. Diversity is, of course, the bastard child of "multiculturalism," i.e., the idea that all cultures and their characteristic "values" are equal. This is an idea that should be resisted by everyone. It was brought home to me by someone mentioning the absurd idea that it is wonderful that there are so many different Christian denominations---as if that were something to rejoice in---and by the presentations at the National Pastoral Musicians convention in Indianapolis in July of last year. There we had contemporary Catholic liturgy served with a large helping of multiculturalism and two scoops of diversity. It was silly.
Look, the only reason why these other Christian bodies exist is because we Catholics didn't do our job right.
If we had fulfilled the mission that Christ gave us at his Ascension, then the world would've been evangelized, the Gospel preached, and those who came to Faith would've been baptized and joined to his body. It is a shame, and it is contrary to the desire of Christ himself (See the Last Supper discourse in the Gospel of John.) Of course, we can't go back and change history, but we should be able to learn from it, you'd think.
The work of Christian ecumenicism is not to rejoice in diversity in the essentials of the Faith. There is no room for diversity in the essentials, that's why they are essentials. The existence of different rites, and spiritualities are diversities of the non-essential variety, and to be gloried in. But the Faith itself is only one, as the Father, Son, and Holy Spirit are one, and for which Christ prayed so earnestly on the night before his death. To pretend otherwise is simply to fall into religious indifferentism, and no Catholic can hold to that.