Here we have to decide whether the original manuscript read abomination (the reading in the printer’s manuscript) or abominations (the 1830 reading). It is possible that the 1830 edition was here set from 𝓞 rather than 𝓟, although the physical evidence itself is indecisive. Elsewhere in the original text, wickedness is normally conjoined with the plural form, abominations (42 times). But in the earliest extant text the singular abomination can be conjoined with wickedness (3 times):
So in theory, either reading (abomination or abominations) is possible here in Helaman 13:17.
There are seven additional cases in the textual history where there is a variant reading between the singular abomination and the plural abominations. One important factor stands out in each of these variants: the error in number always derives from the number of the preceding noun. In other words, if the singular abomination is changed to the plural abominations, the immediately preceding noun is plural, while if the plural abominations is changed to the singular abomination, the immediately preceding noun is singular:
switch from singular to plural
switch from plural to singular
In fact, three of the changes from plural to singular involve the singular word form wickedness (Mosiah 29:18, Alma 37:29, and 4 Nephi 1:39), which suggests that here in Helaman 13:17 the original manuscript read “their wickedness and their abominations” and that abominations was accidentally changed by Oliver Cowdery to abomination when he copied the text from 𝓞 into 𝓟.
If the plural form is the original reading in Helaman 13:17, then we get a series of plural instances of abominations conjoined with wickedness for the larger passage:
But this systematicity is not statistically significant since there are only three firm instances in the earliest text of the singular phraseology “wickedness and abomination” (in contrast to at least 42 instances of the plural phraseology “wickedness and abominations”). Yet it is true that the three singular instances occur as isolates, never in a series of instances.
This evidence, taken in its totality, argues that the original manuscript (and the original text) in Helaman 13:17 read “their wickedness and their abominations”, which means that the 1830 reading is the correct one. The critical text will adopt that reading as the most probable one. This analysis also implies that here in verse 17 the 1830 edition was set from 𝓞 rather than 𝓟, where 𝓞 read in the plural.
Summary: Maintain the 1830 reading in Helaman 13:17, with its plural abominations in the phrase “their wickedness and their abominations”; the singular abomination, the reading in 𝓟, was probably an error introduced by Oliver Cowdery when he copied from 𝓞 into 𝓟.