I think there can be a two step process on this. First, we can learn more about how there is CONTINUITY between the New Testament texts and the later councils and saints. Once that is accomplished, we can show our Protestant friends that their own Bibles teach about fasting, clergy, relics, saints, the intercession of saints, icons, baptismal regeneration, the real presence in the Eucharist, the grace of ordination to the presbyterate, the Theotokos, liturgical worship, incense, confession, binding and loosing, excommunication, the authority of the institutional church, apostolic succession, etc., etc. Moreover, the earliest Christian readers of the New Testament understood the New Testament in this way, all the way up to present-day traditional Orthodox Christians. The distinctive Protestant doctrines (grace alone, faith alone, Scripture alone, anti-saints, anti-sacramental, anti-iconography, anti-relics, etc.) do not appear historically until 14 or 15 centuries after Christ.
The problem is that many American evangelicals have a lot of practice in quoting the Scriptures---and EXPLAINING AWAY what the Scriptures say about commandments and doctrines that Protestants find un-modern and inconvenient. If we read the New Testament texts more carefully than our Protestant friends, then we can point out obvious points that they are not able to see because of modern Protestant indoctrination.
Our Protestant friends have no right to complain about harsh rhetoric. They should be seeking the best arguments against their own prejudices. Those best arguments will be emotionally uncomfortable to read and hear. But if a person is truly interested in what the New Testament actually says, they will welcome hard-hitting arguments that burst bubbles and refute prejudices.
There is also the argument of plain common sense. It was the early Orthodox church saints who were the direct historical successors of Christ's apostles: Clement, Bishop of Rome; Ignatius, Bishop of Antioch; Polycarp, Bishop of Smyrna; Papias, Bishop of Hierapolis, Irenaeus, Bishop of Lyons; etc. The point is that no one seriously denies that these saints taught un-Protestant things. What Protestants then need to admit is that these saints taught what the apostles and the New Testament teach. There is CONTINUITY from Christ to the Apostles to the Orthodox bishops. It is simply common sense that the historical successors of the apostles (the Orthodox bishops) understood their teachers better than Luther and Calvin, fourteen centuries later in a completely different culture. Orthodox Christianity is biblical. In fact, it was the Orthodox Church bishops who put the Bible together in the fourth century (AD 367, 397). Protestantism is a modern movement that is in many ways anti-biblical. It has many anti-supernatural and anti-sacred prejudices. If a person follows the teachings of the Bible, he will believe in fasting, saints, relics, sacraments, icons, incense, church hierarchy, the importance of good works, etc.