It seems to be the case that you would like to have your cake and eat it too.
On the one hand you proclaim "Sola Scriptura," the Bible alone is the sole rule of faith.
On the other hand you have the audacity to tell me (and numerous other christians dating back to the founding of the Church) that our beliefs are wrong, that our Liturgies are wrong. You tell us that they are wrong according to how you (and in reality it is your instructor, who ever that may be...Svendsen, etc.) interpret the Gospel. However, you quickly add the caveat that you are not infallible; but never mind that, we should take your proclamation to be infallible because even with history on our side you have the superior fallible interpretation. How the early Christians practiced their faith is of no relevance to your "Sola Scriptura."
AG's analogy, "It seems to be the case that you would like to have your cake and eat it too," is inapt. It's not applicable to the case at hand. A better analogy here would be "have your orange and eat your apples," for Mr. Greco is comparing not cake to cake but apples to oranges.
AG states, "On the one hand you proclaim "Sola Scriptura," the Bible alone is the sole rule of faith." AG has left out, however, the term "infallible." Scripture is the sole infallible rule of faith. But perhaps this omission is not critical to this particular discussion.
Continuing on, AG states, "On the other hand you have the audacity to tell me ... that [my] beliefs are wrong ... ." There is obviously more to his comment, but this seems to be the key point of his objection. In AG's mind, if one holds to Sola Scriptura, then one cannot tell other people that their beliefs are wrong. This is an incredibly enormous logical misstep. Not only does AG's supposition not follow - it is directly contradicted.
The fact that Scripture is a rule of faith provides a way by which doctrines can be measured. It provides the umpire to settle our arguments. If we disagree over whether Christ died or rose from the dead, we can turn to Scripture and see the answer there. The side who agrees with Scripture teaches the truth.
Where then could AG's non-sequitur accusation come from? I cannot say for sure - logical fallacies sometimes have a way of creeping up on people. I suspect, however, that there is a chance that it has come from AG being overexposed to papist propaganda suggesting that to believe Sola Scriptura is to accept relativism.
Usually the way we see this done is more subtly (such as by pointing out a large number of denominations and then groundlessly blaming this on the standard of Sola Scriptura) but sometimes it is done quite explicitly, even to the point of point an equals sign between Sola Scriptura and relativism.
Of course, all this is absurd: everyone should realize that if one has a standard of absolute truth and that standard is external to oneself, then one is not a relativist. Sola Scripture is a standard of absolute truth and it is external to us. Therefore, those of us who practice Sola Scriptura are plainly not relativists.
And, of course, it is precisely because we recognize that Scripture is the touchstone and metric of doctrinal truth that we can judge whether a church preaches the gospel. If we did not have Scripture as a measuring stick, we'd be left floating in the breeze. Scripture provides an anchor and reference point.
Now, let's deal with a few other of AG's points: "and numerous other christians dating back to the founding of the Church ... ." The label "christian," here is not helpful. If a person claims to be a Christian, but refuses to heed the Word of God, what good is that sort of profession? And the "back to the founding" part of the claim is just absurd. Some of my biggest objections to Catholicism stem, as AG surely knows, from innovations that occurred in history - such as the innovation of papal infallibility, the bodily assumption of Mary, Purgatory, Idolatry, attempted communication with the dead, and Indulgences. Historically, AG doesn't have a leg to stand on.
But furthermore, Paul himself stood up to Christians in his own day - he even opposed a fellow apostle, Peter, to his face. Christians can be wrong, and Christians can and should help to correct each other's errors. Scripture says so.
AG adds that we also tell him that "our liturgies" are wrong. This should be no surprise. The liturgies of Catholicism (and other supposedly ancient religions) have evolved over time. The Roman liturgies ("Latin" rite) are especially famous for the dramatic changes we saw in the Vatican II era - but the others have developed as well. It's not surprising to see them incorporating more or less error over the years, especially in a church that refuses to reform its own teachings to the norm of Scripture.
AG declares, "You tell us that they are wrong according to how you (and in reality it is your instructor, who ever that may be...Svendsen, etc.) interpret the Gospel." This sort of comment is symmetrically reflexive and infinitely regressive. If AG's point is valid, then it is also valid to say that AG tells us that we are wrong according to how he (and in reality it is his instructor, who ever that may be ... Dave Armstrong, etc.) interprets Catholicism's standards. But AG's point is not valid.
We tell him that these things are wrong according to what Scripture says. Scripture, not our interpretation of it, is the standard. We acknowledge the fallibility of our own interpretations, and subject them to the higher authority of Scripture. It's puzzling to me why this concept is so hard for advocates of Catholicism to get.
Don't they know that the law of the land - the thing that determines whether they are committing a crime or not - is not someone's interpretation of the law, but the law itself? In practice, people do have to interpret the law. A judge may have to noodle over the issue of what the law has to say about something, but ultimately it is the law, not the judge, that is the standard. The judge doesn't make his own law: he interprets the law.
The same goes when Christians follow Scripture's commands that require them to be judges of doctrine. Such obedience doesn't require them to become laws unto themselves, but rather to interpret the law of God given in the Word of God.
But AG doesn't stop there. He continues, "However, you quickly add the caveat that you are not infallible; but never mind that, we should take your proclamation to be infallible because even with history on our side you have the superior fallible interpretation." This is just intentional ignorance. How one can add, "But never mind that," knowing that isn't what we say, is simply mind boggling.
Furthermore, of course, history is not on AG's side. As noted above, upon historical examination, numerous central distinctives of Catholicism turn out to be innovations: neither believed nor practiced by the apostles or the earliest churches. History is not the friend of a church that promotes papal infallibility and transubstantiation.
AG concludes, "How the early Christians practiced their faith is of no relevance to your 'Sola Scriptura.'" This is a bit misleading. It is, of course, true that no matter what, Scripture is the norm - not what early Christians did. We know from the book of Revelation that not all the early Christians did what was right.
On the other hand, what the early Christians did is still of interest. Although Scripture is the rule of faith (i.e. the sole infallible authority), the teachings of previous Christians, whether living or passed on, are of value and are not simply to be ignored. That doesn't mean that we automatically accept everything attributed to an early Christian, but it does mean that we read what they wrote, and try to learn from it - all the while comparing it to Scripture - as they would have wanted, as we see in many cases.