Corbin Volluz (personal communication, 15 March 2005) suggests that in this passage the word abominations may be an error for combinations. Both words are phonetically similar. If such an error occurred, it would have happened when Joseph Smith dictated the text to his scribe (here presumably Oliver Cowdery). For this part of the text both 𝓟 and the 1830 edition are firsthand copies of 𝓞; and since both these sources read abominations, we can safely assume that 𝓞 (not extant here) did as well.
There is evidence in the text for both the phrases “secret combination(s)” and “secret abomination(s)”, although there are considerably more instances of the former (22 to 4, excluding the case here in Mormon 8:40). But when the verb is “to build up”, we otherwise get references to building up combinations, never abominations (although in the first case listed below the word combination is not explicitly used to refer to the band of Gaddianton robbers):
Further, two of these passages refer to the purpose of the secret combinations—namely, to get power and gain (Ether 8:23 and Ether 11:15). And Mormon 8:40 also refers to getting gain.
Even so, the example in 4 Nephi 1:42 shows that one can build up secret oaths, which seems less organizational than building up secret combinations. Since secret combinations are associated with both oaths and abominations, building up secret abominations may not be that difficult after all. Further, there is at least one passage that directly lists various abominations (“to commit secret murders and to rob and to plunder”) as leading to gain, although the specific word abomination(s) does not appear:
Heather Hardy has proposed this same emendation for Mormon 8:40 (personal communication, 9 May 2005). And Grant Hardy has provided some additional arguments from similarities in phraseology in arguing for this emendation. He notes, for instance, that in references to the blood of victims and their crying out for justice, all other passages (five of them) refer to secret combinations rather than secret abominations:
Thus the appropriateness of emending secret abominations to secret combinations in the sixth case:
Clearly, there is an obvious connection between secret combinations and secret abominations, and these abominations are committed with the intent to get gain. Thus the use of abominations in Mormon 8:40 is not impossible. Furthermore, it should be noted that there is no evidence in the manuscripts (or the printed editions) that the words abomination(s) and combination(s) have ever been mixed up. The critical text will therefore maintain the occurrence of secret abominations in Mormon 8:40.
Summary: Maintain the occurrence of secret abominations in Mormon 8:40, the reading of the earliest textual sources (𝓟 and the 1830 edition); the reading here is possible since there is a close connection between secret combinations and their secret abominations; the possibility remains that secret abominations here in Mormon 8:40 is an error for secret combinations; if so, it would have occurred as the scribe in 𝓞, presumably Oliver Cowdery, took down Joseph Smith’s dictation.