"Ecumenical" must not mean concealing truth so as not to displease others. What is true must be said openly and without concealment; full truth is part of full love.
"Ecumenical" must mean that we cease seeing others as mere adversaries against whom we must defend ourselves. We have pursued such a course long enough...That we must try to recognize as brothers, with whom we can speak and from whom we can also learn, those who do not share our views. [Fraternal Zeal]
"Ecumenical" must mean that we give proper attention to the truth which another has, and to another's serious Christian concern in a matter in which he differs from us, or even errs. [Give proper attention to the truth which another has, or thinks he has.]
"Ecumenical" means to consider the whole, and not [simply] to single out some partial aspect that calls for condemnation or correction,...[but rather] that we present the inner totality of our faith in order to make known to our separated brothers that...all that is truly Christian...[is innately Catholic].
"Ecumenical" and "Catholic" in their very etymology say the same thing. Therefore, to be a Catholic is not to become entangled in separatism, but to be open to the fullness of Christianity.
Joseph Ratzinger, Theological Hightlights of Vatican II, Paulist Press: New York, 1966, 24. (Google books [Ignatius] edition here). Cf. Gediminas T. Jankunas, The Dictatorship of Relativism: Pope Benedict's Response, Saint Pauls: New York, 2011, 74. Editing of the text (brackets) and emphasis by Plinthos, comparing to the German original as found in Joseph Ratzinger Gesammelte Schriften 7/1: Zur Lehre Des Zweiten Vaticanischen Konzils, Herder: Freiburg, 2012, 315.
P.S. However, we must consider these thoughts in light of the readings for today's ordinary form Mass, especially the Gospel: LK 12:49-53 on Christ's mission of discord!
"I am come to cast fire on the earth; and what will I, but that it be kindled?
...Think ye, that I am come to give peace on earth? I tell you, no; but separation."
The primacy of truth will, ultimately, necessitate separation: Death, the Judgement, Heaven and Hell are absolutely the four last things with which every man must contend!