Initially Oliver Cowdery wrote “all these wickedness” in 𝓞; he soon corrected the plural determiner these to this by supralinear insertion. It is possible to interpret “all these wickedness” as meaning ‘all these wickednesses’, especially since the preceding text implies a plurality in its reference to four types of wickedness: murder, robbery, stealing, and adultery. In Early Modern English, nouns ending in unstressed /ßs/ could be either singular or plural. As discussed under 2 Nephi 31:18, Jacob 4:7, and Alma 34:26, there are instances in the original Book of Mormon text of the nouns witness, weakness, and wilderness that may actually be plurals even though the plural ending -es is lacking. In the same way, it is possible that here in Alma 30:10 the initial text, “all these wickedness”, means ‘all these wickednesses’. Given this interpretation, Oliver’s correction of these to this could have been editing on his part: he just couldn’t accept the apparent contradiction in grammatical number between these and wickedness.
On the other hand, there is no apparent change in the level of ink flow for the correction in 𝓞, which implies that the correction was virtually immediate. Perhaps Oliver Cowdery initially wrote all these simply because he expected a plural after all. But elsewhere in the text, all these is always followed by plural noun forms, including two cases of “all these witnesses” (in Jacob 4:6 and Alma 30:45), not “all these witness” (the parallel that we might expect if “all these wickedness” was the correct reading here in Alma 30:10).
It should also be noted that there is one other occurrence of this wickedness in the text. In that instance, as we might expect, the text refers to a single wickedness:
The critical text will therefore accept the standard reading in Alma 30:10, “all this wickedness”, even though there is a small possibility that the initial reading “all these wickedness” is correct (but only with the meaning ‘all these wickednesses’).
We should also note here that in Alma 30:10 the 1841 British edition accidentally replaced “all this wickedness” with “all his wickedness”, which gives the nonsensical “yea for all his wickedness they were punished”. This use of the determiner his was undoubtedly motivated by the occurrence of the generic he in the preceding text: “and if he committed adultery / he was also punished”. But if the his were adopted, then the following plural pronoun they would have to be emended to he (and the verb were to was), giving “yea for all his wickedness he was punished”.
Summary: Maintain the corrected reading in 𝓞 for Alma 30:10: “yea for all this wickedness they were punished”.