In terms of the written teachings of the Catholic Church, Father James McEvoy is clearly right in insisting that "Rome does not allow Catholics to receive Communion in Protestant churches because full agreement in faith and morals has not yet been reached".
The new Catholic Catechism puts it like this: "Ecclesial communities derived from the Reformation and separated from the Catholic Church have not preserved the proper reality of the Eucharistic mystery in its fullness, especially because of the absence of the sacrament of Holy Orders. It is for this reason that Eucharistic intercommunion with these communities is not possible for the Catholic Church."
The phrase "absence of the sacrament of Holy Orders", highly insulting to most Anglicans, refers to the Catholic belief that at the Reformation the "apostolic succession" handed down to the Church by Christ, through Peter and successive Popes, to be God's authority on earth, was broken. English and Irish Anglican archbishops appointed bishops and priests who were hostile to the Catholic teaching of the Mass.
The Catechism lays down that the only exception to the church's rigid rule forbidding inter-Communion between the Catholics and Protestants is when "a grave necessity" arises and when a non-Catholic, who is, for example, on the point of death, asks for Communion or another sacrament from a priest. However, such a person has to "give evidence of holding the Catholic faith regarding these sacraments". This is rather like asking an Ulster Presbyterian to recognise the authority of the Pope.
The Dungannon priest, Monsignor Denis Faul, agrees completely with Prof McEvoy. In fact he goes further by saying that even when an Anglican's priest has valid orders, a Catholic cannot take Communion from him (or her).
A priest's right under Canon Law to say Mass and offer the Eucharist comes, through his bishop, from the Pope, he says. It is the Pope who, under God, has authority over all the sacraments.
At the Reformation, Mgr Faul goes on, the main Protestant attack was on "the Mass and the unity of the Catholic Church as represented by the Eucharist and the Pope".
"The Protestant reformers rejected the Catholic teaching that the bread and wine of the Eucharist at the heart of the Mass are changed into the living, risen and glorious body of Christ, really, truly and substantially present and offered in sacrifice.
"My friends in the Shankill Road and Sandy Row are better theologians than some distinguished Irish Catholics," he says. "Their theology is perfect on this. They highlight the central points of our religion, the Mass and the Pope. If you have `no Pope here' you'll have a free-for-all in regard to the sacraments."
The other problem with the President taking Communion in a Church of Ireland cathedral, he says, is that it gives a bad example which damages the unity of the Catholic Church, and that could eventually lead to another Protestant-style split.
"We have, thank God, one Catholic Church whereas there are over 500 Protestant churches."
Mgr Faul says the President compares badly with President Robinson and his local unionist MP, Ken Maginnis.
The last president, a Catholic married to a member of the Church of Ireland, never asked if they could receive Communion in the Church of Ireland "as a family".
"Mary Robinson and I disagreed about everything," he says. "But she had dignity, she kept her distance, she treated the Eucharist with respect."
Similarly Ken Maginnis, who attends occasional Catholic funerals and enthronements of Catholic archbishops of Armagh, has "great respect for our Eucharist by not receiving it. We admire him for that. We would like Mary McAleese to show the same respect for the Protestant Eucharist by not receiving it."
Not surprisingly, the outspoken liberal theologian, Father Gabriel Daly, has an utterly different viewpoint. He questions Prof McEvoy's allegation that President McAleese might be "pursuing any private agenda".
"Surely he is not suggesting that the President of Ireland, on taking up office, is no longer free to follow her conscience in matters of religious worship?" he asks.