If there had to be one issue that gets traditionalists upset more than any other, it is “ecumenism.” I see this word tossed out there all the time to mean all sorts of different things–but rarely, if ever, what it actually is and means.
Frist it bears pointing out that “ecumenism” has nothing to do with pagans/infidels. It only deals with the “Reunion of Christendom” or, in other words, bringing the stray sheep back into the one fold. This of course is a very good thing.(Evangelization, on the other hand, deals with bringing the Holy Gospel to infidels and interreligious dialogue should be to this end; see Dominus Iesus).
On the other hand, there are movements out there which can be called “pan-Christian” movements. These seek to create a kind union which is more of a “being-together” of all who profess faith in Christ united around the lowest common denominator. There are also movements out there that might be deemed pan-religious. These are usually the kind of things branded as “ecumenism” which get traditionalists riled up–and rightfully so. But, because they mislabel it, it tends to make them reject even authentic ecumenism. Sadly, there are many Catholics who do embrace pan-Christian or pan-religious beliefs and movements, but they go against the rule of faith as constantly expressed in the past up through the present.
Here are some good readings (but by no means an exhaustive list) for those who wish to get a better understanding of what authentic ecumenism is versus what it is not. In that way, real issues can be discussed in a meaningful manner rather than just throwing out buzzwords without a proper understanding of them:
Here is an overview of ecumenism through 1909 from the Catholic Encyclopedia (it’s a very interesting read): Union of Christendom
Here are papal and concillar decrees concerning authentic ecumenism:
Leo XIII, Praeclara Gratulationis Publicae (The Reunion of Christendom) June 20, 1894
Second Vatican Council, Unitatis Redintegratio (Decree on Ecumenism), November 21, 1964
John Paul II, Ut Unum Sint (On Commitment to Ecumenism) May 25, 1995
And here are some concerning the false pan-Christian movement (of course, the above also deal with false “unions” and movements, but it is the primary focus of the following):
Pius XI, Mortalium Animos (On Religious Unity) January 6, 1928
I can’t find it online, but in Denzinger’s Sources of Catholic Dogma (my edition is from 1954) there is a letter from the Holy Office under Bl. Pius IX concerning Christion Union. It is a really good treatment concerning what is, and what is not, acceptable ecumenism.
Likewise, it bears pointing out that often times traditionalists are very upset by the methods of bringing non-Catholics into the fold used by recent popes. They see the anathemas and harsh condemnations of previous popes compared with the use of more friendly conferences lately and they become confused. The reasons for this less harsh policy are discussed briefly here (as well as in the more recent documents cited above):
Leo XIII, Testem Benevolentiae Nostrae (Virtue, Nature and Grace, and Americanism) January 22, 1899
“But if, among the different ways of preaching the word of God that one sometimes seems to be preferable, which directed to non-Catholics, not in churches, but in some suitable place, in such wise that controversy is not sought, but friendly conference, such a method is certainly without fault. But let those who undertake such ministry be set apart by the authority of the bishops and let them be men whose science and virtue has been previously ascertained. For we think that there are many in your country who are separated from Catholic truth more by ignorance than by ill-will, who might perchance more easily be drawn to the one fold of Christ if this truth be set forth to them in a friendly and familiar way.”