Last Sunday, for example, I preached through Paul’s vice list in Romans 1:29-31. The traditional text lists 23 items. The modern critical text, however, lists only 21. The modern text omits "fornication" (porneia) in Romans 1:29 and "implacable" (aspondous) in 1:31.
Metzger’s Commentary (pp. 506-507) addresses the omission of porneia in v. 29 but only gives it a "C" reading. He notes that "The Textus Receptus, following L Psi 88 326 330 614" and the Majority include the word before poneria ("wickedness"). He admits that one might well argue that porneia fell out accidentally in transcription given its similarity to poneria, but he concludes, "it is more likely that the word is an intrusion into the text…." No substantial reason is provided as to why this conclusion is more likely.
Metzger’s Commentary does not address the omission in v. 31, even though it too has significant attestation in the corrected hand of Sinaiticus, C, Psi, 33, the Vulgate, and the Majority. Given that all the other words in v. 31 also begin with the negative prefix alpha one could easily see how it might have been accidentally omitted in transmission.
Conclusion: There seems to be no outstanding reason not to maintain the traditional-ecclesiastical text and affirm 23 items in Paul’s catalogue of vices. Most modern translations simply omit the two items with no reference or footnote (cf. NIV, RSV, RNRSV, ESV).