The fact that this document is a forgery is not debated by Catholics. The point that you people try to make is that the entire doctrine of the papacy hinges on and/or was created due to this forged document. This could not be further from the truth. Anyone who would hold to this belief is either grossly misinformed or just plain dishonest in their portrayal of the Catholic Church and the papacy.
In order for these claims to be true, then the papacy and all evidence of a Petrine Primacy and succession of such must come after 750 850 A.D. The following evidence shows that such teachings came earlier and totally discredit anyone who would hold that the "Donation of Constantine" is the basis for the papacy.
The following is from The E.F.C. by Jurgens
A.D. 220 Tertulian: "
that the power of binding and loosing has thereby been handed on to you, that is to every church akin to Peter? What kind of man are you, subverting and changing what was the manifest intent of the Lord when He conferred this personally upon Peter? On you, He says, I will build my Church; and I will give to you the keys, not to the Church; and whatever you shall have bound or you shall have loosed, not what they shall have bound or they shall have loosed. " [Modesty, qtd in Jurgens 387]
A.D. 190/210 St. Clement of Alexandria: "Nor does the kingdom of heaven belong to the sleeping and the lazy; rather, the violent take it by force
On hearing these words, the blessed Peter, the chose, the pre-eminent, the first among the disciples, for whom alone with Himself the Savior paid the tribute, quickly grasped and understood their meaning." [Who is the Rich Man That is Saved? qtd in Jurgens 436]
A.D. 226 232 et postea - Origen: "Peter, upon whom is built the Church of Christ, against which the gates of hell shall not prevail, left only one Epistle of acknowledged genuinity. Let us concede also a second which, however, is doubtful." [Commentaries on John, qtd in Jurgens 479a] (This was a comment on the epistles of St. Peter, which later were both confirmed as genuine. As a side note, this discredits those who adhere to sola scriptura as well, since here, two centuries after Christ, they are still debating which books belong to the Canon of Sacred Scripture).
A.D. 244 Origen: (Speaking about Peter) "Look at the great foundation of the Church, that most solid of rocks, upon whom Christ built the Church! And what does the Lord say to him? O you of little faith, He says, why did you doubt! (Matt. 14:31)" [Homilies on Exodus, qtd in Jurgens 489]
A.D. 251 St. Cyprian of Carthage: "The Lord says to Peter: I say to you, He says, that you are Peter, and upon this rock I will build My Church, and the gates of hell will not overcome it. And to you I will give the keys to the kingdom of heaven: and whatever things you shall bind on earth shall be bound also in heaven, and whatever you loose on earth, they shall be loosed also in heaven. | first edition | And again He says to him after His resurrection: Feed my sheep. On him He builds the Church, and to him He gives the command to feed the sheep; and although He assigns a like power to all the Apostles, yet He founded a single chair, and He established by His Own Authority a source and an intrinsic reason for that unity. Indeed, the others were that also which Peter was; but a primacy is given to Peter, whereby it is made clear that there is but one Church and one chair." [The Unity of the Catholic Church, qtd in Jurgens 555-556]
A.D. 254 St. Cyprian of Carthage: "You have written also that on my account the Church now has a portion of itself in a state of dispersion. In truth, the whole people of the Church are collected together and made one and joined to each other in an indivisible harmony. They alone have remained outside who, were they within, would have to be ejected.
And the Lord too, in the Gospel, when the disciples abandoned Him while He was speaking, turned to the twelve and said, And do you too wish to go away? Peter answered Him saying, Lord, to whom shall we go? You have the word of eternal life: and we believe that you are the Son of the Living God.
There speaks Peter, upon whom the Church would be built, teaching in the name of the Church and showing that even if a stubborn and proud multitude withdraws because it does not wish to obey, yet the Church does not withdraw from Christ. The people joined to the priest and the flock clinging to their shepherd are the Church." [Letter of Cyprian to Florentius Pupianus, qtd in Jurgens 587]
A.D. 306 373 St. Ephraim: "Simon, My follower, I have made you the foundation of the holy Church. I betimes called you Peter, because on you will support all its buildings. You are the inspector of those who will build on earth a Church for Me. If they should wish to build what is false, you the foundation, will condemn them. You are the head of the fountain from which My teaching flows, you are the chief of My disciples. Through you will I give drink to all peoples. Yours is that life-giving sweetness which I dispense. I have chosen you to be, as it were, the first-born in My Institution, and so that, as the heir, you may be executor of my treasures. I have given you the keys of My kingdom. Behold, I have given you authority over all My treasures!" [Homilies, qtd in Jurgens 706]
A.D. 461 St. Leo I: "From the whole world only one, Peter, is chosen to preside over the calling of all nations, and over all the other Apostles, and over the Fathers of the Church. Thus, although among the people of God there are many priests and many pastors, it is really Peter who rules them all, of whom, too, it is Christ who is their chief ruler. Divine condescension, dearly beloved, has granted to this man in a wonderful and marvellous manner the aggregate of its power; and if there was something that it wanted to be his in common with other leaders, it never gave whatever it did not deny to others except through him. [Sermons, qtd in Jurgens 2191]
Circa A.D. 391 430 St. Augustine of Hippo: "Before His suffering the Lord Jesus Christ, as you know, chose His disciples, whom He called Apostles. Among the Apostles almost everywhere Peter alone merited to represent the whole Church. For the sake of representing the whole Church, which he alone could do, he merited to hear: I will give to you the keys to the kingdom of Heaven." [Sermons, qtd in Jurgens 1526]
The Donation of Constantine written in the first place Was notto shore up the papacy. No, on the contrary, it was to "support the local bishops against their metropolitans and other authorities, so as to secure absolute impunity and the exclusion of all influence of the secular power." (Dollinger, qtd ).