The OP has a point, for as
@HTacianas pointed out, it is true there are False Gospels as St. Paul warns in Galatians 1:8-9, specifically, in Greek, St. Paul used a word that can mean “traditioned” so the verses can be read that if anyone preaches against the Gospel handed down from the Apostles and thus the Early Church, essentially, the traditional theology of the Christian Church we find expressed most clearly in the liturgical churches, such as Eastern Orthodox, Oriental Orthodox and Continuing Anglicans of the Anglo Catholic persuasion, some of whom recognize seven sacraments (I am curious if my friend
@Shane R falls into this category).
Thus, building on the above, one of the ancient heresies that preached a false gospel was Marcionism, founded by a shipping tycoon named Marcion who unsuccessfully tried to buy his way into the Roman Church, who refunded his donation after he began preaching his heretical doctrine, that the God of the Old Testament was different from the Father of Jesus Christ. Later he published his own “bible” consisting only of mutilated versions of the Gospel of Luke and some of the Pauline Epistles with all references to the Old Testament eliminated, which is ironic, since the authentic Gospel of Luke concludes with our Lord revealing that the entire Old Testament is about Him. Likewise the Gnostic heretics believed that God in the Old Testament was an incompetent demiurge who created the material world, which is a prison which Christ was sent to liberate us from, so we could ascend to the spiritual Pleroma, or fullness.
It is a fact, as
@BobRyan asserted, that there are neo-Marcionists and crypto Marcionists who downplay the Old Testament, because of its prohibitions of homosexuality and other moral transgressions, and they also downplay the Pauline Epistles. These ultraliberal theologians in many cases would probably be most satisfied with a Unitarian Universalist sort of false gospel, something like the Jefferson Bible, Thomas Jefferson’s grotesque edit of the canonical Gospels into what is called a Gospel Harmony, which makes the mediocre Diatessaron edited by Tatian before the latter embraced Gnosticism and founded his own cult, which was used by Orthodox Syriac speaking churches in the East until the translation of the Vetus Syra*
Conversely, we also have the problem of Christians who overvalue the Old Testament relative to the New and forget what St. Luke wrote in his inspired Gospel, that the risen Lord Jesus Christ showed the Apostles how the Old Testament, the Law and the Prophets as our Lord tends to call it, is entirely a prophecy concerning His incarnation, passion and resurrection. This corresponds to certain sects in the Early Cnurch like the Ebionites, who insisted on observing the entire Torah, contrary to Acts 15, also written by St. Luke interestingly enough. Whereas the Gospel of Mark tells the basic story of the Incarnation, and the Gospel of Matthew shows where the events of the Incarnation were prophesized, and the Gospel of John reveals who Jesus Christ is, being a work of high theology and Christology, it is the Gospel of Luke and the Acts of the Apostles that, written in beautiful Greek with Luke 1 and 2 containing the wonderful songs known as the Evangelical Canticles sung at Morning and Evening Prayer in the Anglican, Roman and Orthodox traditions, the
Benedictus, Magnificat, and
Nunc Dimitis, that is also most useful when it comes to correcting errors and also the heresies spread by wolves in sheeps’ clothing, as our Lord calls them. For example, the rejection of the veneration of the Theotokos is refuted by the
Magnificat, and a non-Christological reading of the Old Testament is refuted by Luke 24:25-49
*This was the Old Syriac translation of each of the four Gospels, supplementing the Syriac Aramaic Old Testament included in the Peshitta but dating from the second century, and the Aramaic Targumim, which were interpreted paraphrases originally read in the Synagogues during the Second Temple era after the Hebrew scriptures were read, as the Jews by that time no longer used Hebrew as a vernacular language and predominantly spoke and understood Aramaic.
The Vetus Syra Gospels are particularly interesting because unlike the Peshitta, the main Syriac Bible which mostly agrees with the Byzantine text type, they follow the Western Text Type also used by the Vetus Latina, the original translation of the Septuagint (the Greek translation of the Old Testament) and the Greek New Testament into Latin, which was mostly replaced by the Vulgate translated from Henrew, Aramaic and Greek by St. Jerome, due to the transition from Classical to Vulgar Latin and a desire for a more robust translation. However, parts of the Vetus Latina remain staples of the liturgy of the Western Church even today, for example, “Gloria in Excelsis Deo,” from the Latin mass, and also a prominent feature of a popular Protestant Christmas hymn, is from the Vetus Latina, as the stylistic elegance of its Classical Latin far outshines the Vulgate rendering of the same “Gloria in Altissimus Deo.”
Of course, the differences between the three ancient text types (all of which refer to the New Testament), the Western, the Byzantine and the Alexandrian, are frankly overblown, and the historical dominance of the Byzantine text type due to the KJV and its use in the Greek Orthodox Church and influence on the Peshitta, the Coptic Bibles and the Vulgate, is not to be fretted about; neither is the current preference among translators for the “Minority Text” which is to say the Alexandrian text type derived from three manuscripts, that much to be concerned with, since the differences are subtle. A much more severe problem with some recent translations like the NRSVue is politically correct translation which is inaccurate on the basis of Formal Equivalence, but sneaks in through the back door opened by accident through the initially well intentioned approach of Dynamic Equivalence, but of course the latter is truly valid only when it agrees with the former, and merely renders certain phrases and idioms in a manner more comprehensible in modern languages.