To begin with, he doesn't really explain what he means by the term "Fundamentalist". The term, as it was originally coined, referred to those conservative Protestants that, in response to modernist tendencies, especially in mainline Protestant denominations, posited that there were five fundamental (one might even say "minimal") beliefs that Christians had to adhere to:
1. The inspiration and inerrancy of Scripture
2. The deity of Jesus Christ
3. The virgin birth of Christ
4. The substitutionary, atoning work of Christ on the cross
5. The physical resurrection and the personal bodily return of Christ to the earth
The term "Fundamentalist" was later (beginning in 1979, around the time of the Iran hostage crisis) applied to radical Moslems, and then later to just about any conservative expression of any religion. I don't think this broadening of the meaning of the term was an accidental move. It was an attempt to associate conservative Christians, like Jerry Falwell and his group "The Moral Majority" with the likes of the Ayatollah Khomeini and Osama bin Laden, and this was done for domestic political purposes. The term has thus really ceased to have much meaning, aside from those who wish to use it as a synonym for "stupid," and that seems to be the primary level of meaning with which Dr. Demacopoulos is using the term.
Dr. Demacopoulos makes a loose connection with the original meaning of the term when he says: "Like other fundamentalist movements, Orthodox fundamentalism reduces all theological teaching to a subset of theological axioms and then measures the worthiness of others according to them." The only problem with this statement is that he provides no examples, and the statement is simply not true. If we take, for example, the Greek Old Calendarists, which would be among the most likely candidates to fall into the category that Dr. Demacopoulos is speaking of, you could say that the Calendar issue is used by them as a litmus test issue, but it is hardly the case that they would argue that one needed to only be on the Old Calendar to satisfy their definition of fidelity to Orthodoxy. In fact, the fault the Greek Old Calendarists have, is not that they have a minimalist understanding of Orthodoxy, but that they are maximalists who take some issues which should not be matters over which one should be willing to break communion over, too far. Even among the Old Calendarists themselves they have further divided over many issues. So in fact, their tendency is exactly the opposite of Protestant Fundamentalists, who really were focusing on the minimum one had to believe. And it is actually the Orthodox modernists who typically try to reduce the "essentials" of the Orthodox Faith to the lowest common denominator, and so they are far closer to being fundamentalists in the original sense of the term.
Dr. Demacopoulos then asserts: "The key intellectual error in Orthodox fundamentalism lies in the presupposition that the Church Fathers agreed on all theological and ethical matters." This lazy straw man caricature is not what one would expect of professor of theology at a respected university. If that is the key intellectual error, I would like to find one example of a person who actually fits that description. I doubt that even the slug-nuttiest Old Calendarist that one might find would argue that "the Church Fathers agreed on all theological and ethical matters."
We are then told that "Typically, this manifests itself in accusations that individuals, institutions, or entire branches of the Orthodox Church fail to meet the self-prescribed standard for Orthodox teaching." I would be curious to know why St. Mark of Ephesus would not be considered an "Orthodox Fundamentalist," because he broke communion with those who failed to meet what St. Mark considered to be the standard for Orthodox teaching. Probably, the answer we would get is that St. Mark was not a intellectual troglodyte, but regardless, there obviously are boundaries that can be crossed that warrant such an action, and so the issue is not whether someone is a fundamentalist because they believe there are such boundaries, but rather the merits of the specific issues at stake... which we are not provided with in this article.
He then goes on to provide examples that knock down the straw man he has set up:
"Indeed, a careful reading of Christian history and theology makes clear that some of the most influential saints of the Church disagreed with one another—at times quite bitterly. St. Peter and St. Paul were at odds over circumcision. St. Basil and St. Gregory the Theologian clashed over the best way to recognize the divinity of Holy Spirit. And St. John Damascene, who lived in a monastery in the Islamic Caliphate, abandoned the hymnographical tradition that preceded him in order to develop a new one that spoke to the needs of his community."
Here again, we find careless overstatements. Where do we find St. Peter and St. Paul disagreeing over circumcision? We find them in very clear agreement on that issue in Acts 15. Most likely, he has in mind Galatians chapter 2, but the disagreement was not over circumcision... it was over St. Peter's hypocrisy while around those "of the circumcision" -- there is no indication that they had a substantive disagreement on the issue. They had a disagreement over St. Peter's behavior and inconsistency, and St. Paul called him on it, to his face, and in the presence of all (Galatians 2:11,14). There is also no indication in the text, nor in Church Tradition that this was a matter of ongoing disagreement or division between these two saints. This was rather an example of even a great saint being capable of falling into temporary error.
It is also clearly excessive to claim that St. John of Damascus "abandoned the hymnographical tradition that preceded him". What was the hymnographical tradition that preceded him? The way older aspects of the services have generally ended up being sidelined was not usually by them being replaced by new hymns, but rather by being supplemented with newer hymns, and then as time went on, some of the older texts were generally omitted. If you take the introduction of the texts we use now for the canons at Matins, these hymns were originally sung with the Biblical Odes, which were the older texts that preceded the composition of those hymns. Only as time went by did the practice develop of generally omitting the odes, and retaining the troparia that were composed to be sung with them (though the older practice is still followed to some extent on the weekdays of Great Lent). So to suggest that St. John tossed out all that preceded him is simply contrary to fact.
Also, there is a wee difference when a holy man, such as St. John of Damascus, introduces some new liturgical practice, than when a committee of cigar smoking "theologians" does so. For example, the Greek practice of saying "With the fear of God and with faith and love, draw near" is clearly a change from the original form of "With the fear of God and with faith, draw near". But it was, I believe, introduced by the Kollyvades Fathers. I was told by someone who is a good source on the matter that St. John of Shanghai also followed this practice. I am inclined to bow to the wisdom of these saints, but think it is right to be skeptical of changes that are introduced by someone who may be very intelligent, but who is not in the same league as these saints.
We find even further hyperbole when Dr. Demacopoulos asserts: "It is important to understand that Orthodox fundamentalists reinforce their reductionist reading of the Church Fathers with additional falsehoods. One of the most frequently espoused is the claim that the monastic community has always been the guardian of Orthodox teaching. Another insists that the Fathers were anti-intellectual. And a third demands that adherence to the teachings of the Fathers necessitates that one resist all things Western."
While it is true that monastic communities have generally been bulwarks of Orthodoxy, I don't know of anyone who would say that this has always and invariably been so. I doubt a single example could be produced of anyone who would seriously argue that the Fathers were anti-intellectuals. And the closest example of one who argues that the teachings of the Fathers necessitates that one "resist all things Western" would be Fr. John Romanides, and his admirers... but not even they would make such a sweeping statement as is made here, and I don't think Fr. John Romanides was an anti-intellectual.
And when Dr. Demacopoulos makes the assertion that "By repurposing the tradition as a political weapon, the ideologue deceives those who are not inclined to question the credibility of their religious leaders", it would be helpful if he would provide some examples and name some names so that we would have some idea of who and what he is referring to.
Furthermore, I am not so sure that "The significance of the Fathers lies in their earnest and soul-wrenching quest to seek God and to share Him with the world." If that were the case, I am not sure how they would be any different than Lao Tzu, Gautama Buddha, Socrates, or Muhammad. Their significance is in how they explained, articulated, passed on, and earnestly contended for "the Faith once delivered unto the saints" (Jude 1:3). They were not just smart men who were earnest, but holy men who received the Faith of the Apostles, and passed it on without alteration -- and in doing so, in the face of new challenges to that Faith, enriched the Church with their words, their faithful lives, and their examples. We understand the Faith better because of them, but we do not now have a new faith or a different faith.
And he closes with this call to action: "It is time for Orthodox hierarchs and lay leaders to proclaim broadly that the endearing relevance of the Church Fathers does not lie in the slavish adherence to a fossilized set of propositions used in self-promotion." But I don't see how Orthodox hierarchs or lay leaders can answer his call, even if they were inclined to do so, because Dr. Demacopoulos gives us no indication exactly who or what he is talking about.
If someone can be pointed to that is fairly described by the descriptions found in this article, I would certainly think such a person was worthy of criticism. But let's talk specifics, rather than tossing around meaningless terms that would have us believe that there is real line of philosophical agreement between the average conservative Evangelical Protestant, some unspecified group of Orthodox Christians, and Jihadist terrorists that are beheading and stoning those they disagree with.
Update: Someone referred me to the conference that Dr. Demacopoulos was apparently referring to. There was a conference (entitled "Patristic Theology and Post-Patristic Heresy") held in Piraeus, Greece, on February 15, 2012, which was at least in large part in response to the Volos conference he mentioned. Among its speakers were Protopresbyter George Metallinos, Professor Emeritus of Athens University, and Metropolitan Hierotheos (Vlachos). Are these really the "Orthodox fundamentalists" who claim that the Fathers were anti-intellectual, and agreed on all points of theology and ethics? You can read their papers, among others, in a pdf format, by clicking here and clicking here.