In an earlier post, How to validate a theory of Bezae’s text, I suggested a fourfold classification of the nine theories of the so-called “Western” text enumerated by B. M. Metzger in his Textual Commentary.  The four categories are:
- Multiple editions
- An initial “Western” text
- A secondary “Western” text
- Assimilation to either the Latin or Syriac versions
(Of course, reference to the “Western” text is somewhat problematic given the existence of multiple “long texts” of Acts. Therefore I will consider these theories from the point of view of the single extant text of Codex Bezae.)
It is evident that the first three classes of theories focus on the timing of the development of the “Western” tradition with respect to the mainstream tradition — whether it came before, after, or roughly contemporaneously with the mainstream. Theories of assimilation also presume that the “Western” text is secondary, but go further in attributing the development of this text form to a specific source of influence, namely, a desire to conform the Greek text to a more familiar versional text.
Now the consensus is not favorable to theories that Bezae’s Greek text reflects systematic assimilation to a version, in particular, to the Latin version. As Metzger plainly observes:
“The theory finds little or no support among present-day scholars.” 
It seems though that most theorists since the eighteenth century have considered the question primarily in terms of the interaction of Bezae’s columns, where it has been shown that assimilation to the Latin column cannot explain the development of the present Greek column. Framed in these terms Latin assimilation is easy to dismiss.
But as I have argued in “Has Latin influence on Bezae’s Greek text been disproved?” and “Against reason? Bezae’s Greek text and the possibility of Latin influence,” interaction between the columns is just one aspect of the question of Latin influence. A second, more fundamental aspect is whether Bezae’s Greek text has been corrected to one or more Old Latin exemplars besides its Latin column.
Once this bigger picture is considered, the theory of assimilation to the Old Latin begins to offer what other theories for the most part lack, namely, a specific, documented historical context and, more importantly, a compelling motive for the effort and expense of producing a Greek text form that so often mirrors the Old Latin version. This motive was simply the belief among certain of the participants that the Old Latin version was less corrupt than the Greek. Thus, in his Commentary on Romans 5:14, we find Ambrosiaster arguing that the text form found in his Old Latin manuscript, lacking the negative particle, is in fact the correct reading, while the Greek manuscripts that have the particle are corrupt.
Nevertheless, it has often been considered next to impossible that the ancient producers of a Greek text would borrow from a Latin version. H. Marsh argues:
“I have myself collated the two first chapters of St. Mark … and have found that in most of the readings, in which the Codex Bezae differs from all the Greek manuscripts, it agrees with some one of those Latin versions. But shall we therefore conclude that those readings were actually borrowed from a Latin version, and translated into Greek? It is at least as possible that they might have had their origin in the Greek as in the Latin, and this very possibility is sufficient to defeat the whole of Wetstein’s hypothesis [that Bezae borrows Old Latin readings].” 
“there is no reason whatsoever for ascribing any reading of a Greek manuscript to the influence of the Latin, unless it can be proved that it could not have taken its rise in the Greek, and that it might easily have originated in the Latin” 
Although Marsh acknowledges the abundant evidence and correctly infers what the evidence seems to imply, he simply assumes that no one would ever want to correct a Greek MS to a Latin MS. Perhaps more tellingly, he speaks of readings being borrowed and translated or having an origin as though these events took place in a vacuum. Of course, what is missing from Marsh’s account is any attempt to recover the perspective of the human participants or even to acknowledge that human actors exist.
Yet going back to Ambrosiaster’s argument, it is obvious that a corrected Greek MS without μη would show not a trace of having been inspired by the Latin reading. The absence of the particle really leaves no definitive argument as to why it might be lacking. Certainly, Latin influence is not the most compelling explanation for a missing particle. So by Marsh’s rule we have no reason to suspect Latin influence. Yet we have a documented case of an unambiguous motive to drop this very Greek particle in accordance with the Old Latin variant. The motive of course is that the Old Latin version was regarded as preserving the true text, but the Greek was seen as corrupt.
But can there be any more compelling motive for the correction of a Greek MS than the belief that it was simply wrong?
It turns out then that the compelling aspect of assimilation theories is the human aspect and, in particular, the practically limitless human capacity to insist that what is familiar must be correct. Clearly, human participants are dangerous to text-critical theories based on pure reason. Once they are allowed into the picture, assimilation theories that were once judged impossible by the standards of criticism are suddenly not so improbable and in the proper context even compelling.
 B. M. Metzger, Textual Commentary on the Greek New Testament (2d ed.; Stuttgart: Deutsche Bibelgesellschaft, 1994) 223-232.
 Metzger, Textual Commentary, 231.
 H. Marsh, “Notes” in J. D. Michaelis, Introduction to the New Testament (trans. H. Marsh; 1802) 2/2:680-681.
 Marsh, “Notes,” 2/2:683. J. S. Semler likewise considers it “against reason” that a Greek MS would be corrected to a Latin copy. J. S. Semler, Apparatus ad liberalem Novi Testamenti interpretationem (1767) 44.