This is a question to those who oppose all ecuмenism, even in principle, or who consider the attempt heretical.

Doesn't the example of the safe conduct given in Trent (below) serve as a historical precedent for the ecuмenism of the return? Despite by all appearances being obstinate in their heresies, the Protestant leaders were invited to Trent for theological discussions because the Church graciously wanted to reclaim the erring.

So just as the Church did then, why not today? In addition to attempting individual conversions, an authentic ecuмenism can be profitable to the Church for the return of leaders or whole communities. Also, it seems to me that in this age, when help from the secular arm is out of the question, it is the only practical way to effect corporate reunion as such. The Greek and Russian schismatics alone count some 300 million souls, so is it not worth considering in principle?

Trent:

But since those of the glorious province of Germany, who call themselves Protestants, desire to be heard by the holy council in regard to these articles before they are defined, and for this reason have asked of it a pledge that they may be permitted to come here in safety, sojourn in this city, speak and express freely their views before the council and then depart when they please, this holy council, though it has for many months looked forward with great eagerness to their arrival, nevertheless, like an affectionate mother that groans and labors, desiring and laboring tirelessly to the end that among those who bear the Christian name there may be no schisms, but that as all acknowledge the same God and Redeemer, so also may they confess the same, believe the same, know the same, trusting in the mercy of God and hoping that they may be brought back to the most holy and salutary union of one faith, hope and charity, willingly yielding to them in this matter, has, so far as it concerns [the council], given and granted, in accordance with their request, assurance of safety and good faith, which they call a safe-conduct ...

... to each and all priests, electors, princes, dukes, marquises, counts, barons, soldiers, the common people, and to all other persons of whatever state, condition or character they may be, of the German province and nation, to the cities and other places thereof, and to all other ecclesiastical and secular persons, especially those of the Confession of Augsburg, who shall come or be sent with them to this general Council of Trent, and to those who are going to come or have already come, by whatever name they are or may be designated, to come freely to this city of Trent, to remain, abide and sojourn here and to propose, speak and consider, examine and discuss any matters whatever with the council, and to present freely whatever they may think suitable, to set forth any articles whatever either in writing or orally, and to explain, establish and prove them by the Sacred Scriptures and by the words, decisions and arguments of the blessed Fathers, and also to reply, if need be, to the objections of the general council, and to dispute and confer charitably and respectfully and without hindrance with those who have been selected by the council, reproachful, vexatious and offensive language being absolutely put aside; and particularly, that the controverted matters shall be treated in this Council of Trent in accordance with Sacred Scripture and the traditions of the Apostles, the approved councils, the consensus of the Catholic Church and the authority of the holy Fathers; with this further addition, that they shall under no condition be punished by reason of religion or of offenses committed or that may be committed in regard thereto.

...and that on the conclusion of these matters or before their conclusion, whensoever it shall please them, if they should wish by the command and permission of their superiors to return to their homes, or if any one of them should so wish, they may at their pleasure return freely and securely, without restraint, formality or delay, without injury to their property and to the honor and persons of their attendants and vice versa; making known, however, their intention of withdrawing to those to be deputed by the council, so that at a convenient time, without deceit or fraud, provision may be made for their security.

...

All of which it promises and pledges in good faith to be inviolately observed toward each and all of the faithful of Christ, toward all ecclesiastical and secular princes and all ecclesiastical and secular persons, of whatsoever state and condition they may be or by whatsoever name they may be known. Moreover, it promises in sincere and good faith, to the exclusion of fraud and deceit, that the council will neither openly nor secretly seek any occasion, nor make use of, nor permit anyone else to make use of, any authority, power, right or statute, privilege of laws or canons, or of any councils in whatever form of words expressed, especially those of Constance and Siena, in any way prejudicial to this public faith and the fullest security, and of the public and free hearing granted by this council to the above-named; these it abrogates in this respect and for this occasion.

(Sorry, messed up on the last post.)

Nishant, I think you are mistaken. There is a difference between ecuмenism of the return, and the ecuмenism of today. To prove this, read Benedict's own words:

Benedict XVI, Address to Protestants at World Youth Day, August 19, 2005: “And we now ask: What does it mean to restore the unity of all Christians?... this unity does not mean what could be called ecuмenism of the return: that is, to deny and to reject one’s own faith history. Absolutely not!”