Nick01,
Your post is well reasoned; but, IMO does not address my 2 primary points of concern.
1) Sinaticus and Vaticanus, while presumed older, are both Alexandrian.
2 The Alexandrian church was known to practice allegorical interpretation; and the Alexandrian ECF are known for taking liberties with the Word of God to the point that many are considered heretical by sound scholarship.
But neither of these points go to whether a particular manuscript, or even a group of manuscripts, are trustworthy witnesses or not. Are you suggesting the Alexandrian ECFs wrote the manuscripts themselves? Are you suggesting the Alexandrian Fathers were always of one mind, and everyone interpreted the Scripture the same way? And, of course, interpreting Scriptures a certain way is very different to outright changing the text to suit your argument, an assertion that should be made with some sort of evidence, not speculation or arguments of guilt by association.
We have to remember first of all that there is considerable debate by exactly what views the Alexandrian Fathers held, and what they meant by them, and whether they held those views INSTEAD of orthodox interpretations, instead of as a kind of intellectual side project - much of what Clement of Alexandrian has been accused of in terms of allegorical interpretation or outright heresy descends to us via quotations from Photios, centuries later. Photios was explicitly trying to paint Clement as a heretic (for reasons both theological and ecclesiastical - many of the early fathers didn't quite toe the later prevailing line established by Rome), so it's not always clear what it was Clement originally meant - we can't examine some of what he said or wrote in its original context.
But even then, we know, for instance, that there was considerable debate within Alexandria itself about interpretative principles. Theohpilus of Alexandria disagreed with large swathes of Origen's writings. Then, you have people from the Byzantine part of the empire like Gregory of Nyssa who adopted and even evolved some of the more controversial elements of people like Origen (eg. he took Origen's thought about universalism to the next step, and went further than Origen himself ever did). And, of course, the likes of Clement of A and Origen were amongst the frontline apologists against Gnosticism in the early centuries, particularly against people like Valentinus.
The point being (as I said previously),
it's impossible to make generalisations fit individuals. Even if it were, it still doesn't draw a connection between Alexandrians tampering with manuscripts, and even THEN, it's not clear why people would change the texts, and how, given it mattered greatly to them (as is clear if you read even a bit of what Clement of Alexandrian, for instance, wrote) what the apostolic texts actually said and meant to say.
Those codices which are complete or nearly complete from the Syriac, Coptic, and Byzantine churches all include the disputed verses. These manuscripts come from geographically diverse areas all of which practiced literal interpretation.
Allegorical interpretations and unbiblical teaching were as possible in the Eastern empire as much as in the south Mediterranean. cf Marcion, Gregory of Nyssa, Appolinarius, Arius, Sabellius, Theodotus of Byzantium, etc
Also, it depends very much what variants you're talking about when looking at the versions. 1 John 5:7 (the comma) shows up in the Vulgate, and in a small number of late Byzantine Greek texts, but is missing in the Syriac. Similarly, the early Syriac and Coptic VSS don't have the Long Ending of Mark and stop at v8, against the majority of Byzantine texts. Going through such examples, it's always the case that the earliest versions were working from Alexandrian or Western type clusters, not Byzantine. It's only when you get to around the 5th century at the absolute earliest (depending on when you date later versions) that you can start to make the argument that the versions were working from another text. So your above statement is incorrect, unless qualified with examples.
A geographically isolated deletion by a church that practices allegorical interpretation seems more likely to me than geographically diverse additions, all in agreement, by churches that practice literal interpretation.
The problem is that
the Byzantine texts do not agree with each other, either. Again, find me any two Byzantine manuscripts that agree 100%. When we are talking about 'The Byzantine Text', we are not talking about one particular manuscript. We are talking about a statistical amalgamation of texts, accounting for variants and contradictory readings (with a bit of human judgement thrown in for when the statistical analysis produces a tied result). You have to do the precise same work with the Byzantine texts as you do with any other, as even Majority Text scholars know - as I mentioned earlier in this thread, a key reading in Romans 5:1 in the Byzantine tradition is almost exactly split 50% down the middle! That means that half of all the Byzantine MSS are WRONG at that verse. Do we conclude that half of scribes believe the Bible was allegorical and it didn't matter? Or is there are more reasonable theory accounting for the data?
Who is more likely to alter God's Word?:
1) deletions by two transcribers from one city that believes that the Bible generally doesn't really mean what it says
2) additions by seventeen transcribers from 3 locations that believe that the Bible means exactly what it says with a few obvious exceptions.
Loaded question. You have no way of knowing what motivated the transcribers, you have no way of knowing the exact provenance of the manuscripts in question, you are also throwing around numbers of transcribers that you've gotten from I don't know where. The Alexandrian manuscripts don't all come, or indeed were written in, Alexandria itself any more than the Byzantine texts were all written in or come from Byzantium/Constantinople/Istanbul. The names themselves are only generally applicable to geography, and really talk much more about the genealogy of the text (and even then, there's argument about how accurate the demarcations actually are)
And then, of course, as I said before, it goes beyond Aleph and B - the papyrii didn't all come from Alexandria either, and similarly do not represent a Byzantine text type. 'Two transcribers' is just a very inaccurate description of the situation. Obviously, I reject the premise of the question.
My premise is that the former option is more likely regardless of the age of the documents!
And I believe that premise is a more than a little shaky, as I have illustrated.
my two concerns: Geographic isolation vs diversity & allegorical vs literal interpretation
I hope I've pushed back just enough to give you pause for thought on your dichotomies.