In most bibles, Mark 2:14 asserts that “Levi, son of Alphaeus” was the tax-collector sitting in the booth whom Jesus called into ministry.

Metzger says the western ms. saying “James” are assimilating 2:14 with the James of 3:18:

** you do not have permission to see this link ** Leui,n {A}
The reading VIa,kwbon in Western witnesses shows the influence of ** you do not have permission to see this link **, where VIa,kwbon to.n tou/ ~Alfai,ou is included among the twelve.

Textual Commentary, 2nd ed. 5th printing, © 2002

CNTTS lists the evidence for the “James” reading as 

iakwbon ** you do not have permission to see this link ** >>

Under the canon of preferring the more difficult reading, shouldn’t we prefer the “James” over “Levi” for Mark 2:14, on the grounds that scribes likely wouldn’t have confused Levi with James?

Or would it be better to say that the degree of confusion in the early church on Matthew’s relation to Levi, and their relation to James was great enough to warrant supposing some ancient scribe would likely confuse James with Levi?  It is hard to believe Metzger’s excuse, that the “James” reading arose merely because scribes were attempting to assimilate Mark 2:14 with 3:18, as we’d have to believe their desire to assimilate prevailed over their knowledge that Matthew is different than James.

Of course, it may very well be that to the ancient scribes, the calling of Levi from a tax-booth in Mark 2:14 did not equal the calling of Matthew from a tax-booth in Matthew 9:9.  Origen infamously remarked that the only justification for saying Levi was one of the 12 apostles was a textual variant found in one of his copies of the gospel of Mark:

And after such statements, showing his ignorance even of the number of the apostles, he [Celsus] proceeds thus: “Jesus having gathered around him ten or eleven persons of notorious character, the very wickedest of tax-gatherers and sailors, fled in company with them from place to place, and obtained his living in a shameful and importunate manner.” Let us to the best of our power see what truth there is in such a statement. It is manifest to us all who possess the Gospel narratives, which Celsus does not appear even to have read, that Jesus selected twelve apostles, and that of these Matthew alone was a tax-gatherer; that when he calls them indiscriminately sailors, he probably means James and John, because they left their ship and their father Zebedee, and followed Jesus; for Peter and his brother Andrew, who employed a net to gain their necessary subsistence, must be classed not as sailors, but as the Scripture describes them, as fishermen. The Lebes also, who was a follower of Jesus, may have been a tax-gatherer; but he was not of the number of the apostles, except according to a statement in one of the copies of Mark’s Gospel. And we have not ascertained the employments of the remaining disciples, by which they earned their livelihood before becoming disciples of Jesus. I assert, therefore, in answer to such statements as the above, that it is clear to all who are able to institute an intelligent and candid examination into the history of the apostles of Jesus, that it was by help of a divine power that these men taught Christianity, and succeeded in leading others to embrace the word of God.** you do not have permission to see this link **

** you do not have permission to see this link ** NPN, Origen: Against Celsus, book 1, ch. 62

It is interesting that Origen speaks here as if he didn’t know that the calling of Levi in Mark 2:14 is mirrored in Matthew 9:9.  I think Origen wasn’t impressed with the Levi = Matthew solution.

Here’s an ** you do not have permission to see this link ** arguing against the harder-reading canon.