I'd kindly ask you to support your statement by a quotation of a Father, or by a decision of a council. Or at least by a cathehezis.
OK, why not. In order to dissect, and then correct heresy, one must begin with the statement(s) in question.
Your initial statement:
Or you mean forgiveness without repentance, so I become an assistant of what I see unacceptable and actually support what I oppose?
Your follow-up statement:
Forgiveness does not require repentance; in fact, it is a divine quality to give forgiveness without repentance (as Christ did upon the Cross).
a) I don't have Divine qualities.
b) No forgiveness without repentance. The repentance is not required for rightous to be proved right, but to sinner/errer to see his sins/errors.
By forgiving without repentance, a forgiver participates in the committed sin post festum and is supporting and co-authoring future sins.
No compromise on that.
The statement in question which is accused of being heretical per se
is the statement "By forgiving without repentance, a forgiver participates in the committed sin post festum
and is supporting and co-authoring future sins."
Let us diagram the incorrect assumptions and conclusions within the statement:
1) Forgiveness without repentance leads the Forgiver to participate in the committed sin post festum
2) Forgiveness without repentance leads the Forgiver to support and "co-author" future sins.
Now, on the general subject of Forgiveness, we have the following references:
"Peter came to Jesus and asked, 'Lord, how many times shall I forgive my brother when he sins against me? Up to seven times?' Jesus answered, 'I tell you, not seven times, but seventy-seven times (or seventy times seven).'" (Matthew 18:21-22)
"And when you stand praying, if you hold anything against anyone, forgive him, so that your Father in heaven may forgive you your sins." (Mark 11:25)
"Be kind and compassionate to one another, forgiving each other, just as in Christ God forgave you." (Ephesians 4:32)
This doesn't even include the Lord's prayer, which is found in two forms in the scripture, one which asks us to Forgive as we forgive, and another which asks us to Forgive as we forgave.
What about Matthew 6:14-15, which says that if we don't forgive our brethren, then we won't be forgiven?
Finally, on this subject, and the one which flies in the face of your statement, is "Father, forgive them; for they know not what they do," (Luke 23:34) uttered by Christ upon the Cross.
What about Forgiveness? What kind of repentance is required for forgiveness? Christ tells us in Matthew 5:38-45 that nothing
should be required for your love... If someone wrongs you, you should forgive them right away, and if they wrong you again, you should forgive them again.
How about St. Isaac the Syrian's take:
"But I say, if the merciful one is not also beyond justice, he is not merciful. That is, not only from his own part will he be merciful to others, but also he will endure injustice gladly and voluntarily. He will not establish and seek full justice in his dealing with his companion but will be merciful to him; because when he overcomes justice with mercy he will weave for himself a crown, not of those who are just according to the Law, but of the perfect according to the New Covenant."http://www.antiochian.org/node/18185
By making your statement, you have impugned responsibility for sin upon Christ our True God, the Only Sinless One.
Christ was, is, and will always be sinless. (1 Peter 2:22, 1 John 3:5, John 8:46, Isaiah 53:9)
One cannot separate action for us and for Him - Christ, when He walked upon the Earth, lived a righteous life, healed the sick, and forgave those who crucified Him. These actions He did while on Earth, after taking on flesh - how can you say that He is responsible for their sin? How can you say that He supports their future sin? How can you say that He is the co-author of their future sin?
You made a general statement for mankind: that forgiveness without repentance makes the forgiver culpable for the sin, and any future sin. I have shown you that it is not correct in its most important application, and thus is completely false.
What do the sources say about giving forgiveness?
Having looked at the malady of anger, judgment, and resentment, let's go on to look at the cure. What are we to do to be freed of this sickness?
Our Lord Jesus Christ tells us clearly: Love your enemies. Do good to those who hate you, bless those who curse you, and pray for those who spitefully use you. And to him who smites you on the one cheek, offer also the other (Luke 6:2729).
Rather than resenting those who wrong us, we are to love them, and we express this love by blessing them and praying for them. We do this because we are commanded to do so by Christ. He has commanded this for our own sake, for our own salvation, because He loves us; and we do it for His sake, because we love Him. Our fallen nature rebels against this: "What? Bless and pray for that person who wronged me?" But for Christ's sake, we go against our fallen nature, and force ourselves to pray. We ask God to bless and have mercy on the person who hurt us, we wish good things for him, we wish his salvation, just as our Lord wishes his salvation. In this way we begin to become like God Himself, Who, according to the words of Christ, is kind to the unthankful and the evil (Luke 6:35). In going against our fallen nature, we return to our original naturethe image of God in usand we grow in the likeness of God.
Abba Dorotheus, a Desert Father of the sixth century, says that we can be healed of the sickness of resentment "by prayer right from the heart for the one who has annoyed us. We can pray such words as, O God, help my brother, and me through his prayers.'" "In this," says Abba Dorotheus, "we are interceding for our brother, which is a sure sign of sympathy and love, and we are humiliating ourselves by asking help through our brother's prayers. 
When we continually force ourselves to bless and pray for others in this way, we will find that our Lord Jesus Christ will change, renew, and refresh our hearts. It may take some time and persistence, but gradually, almost imperceptibly, we will be changed. The poison of resentment, by the Grace of Christ, will leave our system.
Again our Lord has told us: Judge not, and you shall not be judged. Condemn not, and you shall not be condemned. Forgive, and you shall be forgiven (Luke 6:37).
The cure for anger, judgment, and resentment is forgiveness, pure and simple. No matter what terrible afflictions and unspeakable injustices have befallen us, we can be free of their negative effects on us through forgiveness.
I once asked a Romanian Orthodox priest named Fr. George Calciu about this. For twenty-one years he had been locked in Communist prisons, where he had endured the most unimaginable horrors ever perpetrated by human beings. And yet when I met him here in America, he was happy, joyful, like a child, totally free of any negative effects of this torture on his soul. He had found the secret of forgiveness. I asked him, "How can people overcome judgment?" He looked at me, almost with astonishment, and answered, "It's simple. Just don't judge!"
It's truly simple. But we must keep in mind that we can't do it on our own: We need God's help to heal our fallen, wounded nature, to humble our pride. Therefore, as we pray for those who have hurt us, we should pray that God will help us to forgive, that He will soften our hard hearts, warm our cold hearts, and grant us a loving, merciful, and forgiving spirit.
Elder Sampson (Seivers) of Russia, who reposed in 1979, was a man well-equipped to speak on the subject of forgiveness. As a young novice monk, he was arrested by the Communist authorities, shot in a mass execution, and thrown into a common grave. By Divine Providence he survived the shooting, and was pulled out of the grave still breathing by his brother monks and nursed back to health. Later he was arrested again and spent nearly twenty years in Communist concentration camps. But he never held onto bitterness and resentment: He completely forgave both his executioners and his torturers. In his later years, when he was serving as a spiritual father to many people, he was especially tough when his spiritual children refused to forgive someone, even for some petty annoyance. He said: "I've always concluded: this means that they still have not gotten the point, that the whole secret, that all the salt of Christianity lies in this: to forgive, to excuse, to justify, not to know, not to remember evil.
"The Holy Fathers are the children of the Grace of the Holy Spirit. The result of this action of Grace is when the heart excuses. It loves, it can speak well of someone and pray for him. It does not remember offense or evil.
"Therefore," said Elder Sampson, "it is impossible to forgive and not excuse. This is a psychological fact. The heart is made this way. It was not the brain, not the nervous systemas science attempts to teach, and the psychiatrists especiallybut it was the heart that was made this way by God. It is called a Christian heart. It excuses, it does everything possible in order to justify and excuse. Isn't that so?! That is a Christian quality!
"The pagan or the Moslem does not know about this ... the action of the Grace of the Holy Spirit.... Try telling a Moslem to justify and excuse, to love his enemy. He will kill you. 
Once Elder Sampson was asked, "What can an angry person do?" He replied, "He must pray and pray for healing. For the sake of his faith, for the sake of his insistence, the Lord will change his heart." 
 St. Dorotheus of Gaza, Discourses and Sayings (Kalamazoo, Mich.: Cistercian Publications, 1977), p. 154
 Elder Sampson (Seivers), "Discussions and Teachings of Elder Sampson," The Orthodox Word no. 177 (1994), pp. 21415
 Ibid., p. 224.
There are numerous Patristic quotes on this page: http://www.orthodox.net/gleanings/forgiveness.html
So what's the conclusion: that forgiveness should come readily from our mouths, not only for the salvation of those we forgive, but also for our own salvation. This forgiveness does not mean that one must be accepted into Communion; it does not mean forgetting the errors of the past; it does not mean Spiritual apathy. In the case in point - forgiveness of the RC church for its errors does not mean that we would be in Communion with them, or even accept communion with them; forgiveness has nothing to do with doctrine, Theology, Ecclesiology, or any other sort of discipline. Forgiveness is an exercise of the Soul and Heart and Mind, one which opens the door to the kingdom for those who wield it freely and skillfully.
What do I ask? That you freely forgive anyone who you feel has wronged you, hated you, persecuted your people and your family; pray that they may join you in heaven. Don't allow the wrongs to continue or persist, and do not enter into agreement until people come to the Truth. But don't hold that grudge; for that grudge may do you more harm at Christ's Judgment Seat than it will do them.