Because Mormon is writing this description long after the events, he is interpreting the documents before him. An official report would never cast such a pejorative light on the reigning king. Given that the tone is Mormon’s, it is possible to make a few deductions about the material upon which he was basing his opinions.
Mormon was obviously offended by several qualities of Noah. He did not keep the commandments of God. He had many wives and concubines. He caused his people to commit sin and abominations, or, slightly more specifically, to commit whoredoms and “all manner of wickedness.”
Later in verse 6, Mormon adds idolatry to the catalogue of Noah’s sins. Except for sexual immorality, it is not clear what specific behaviors Mormon was capturing with his terms “sin,” “abominations” and “all manner of wickedness.” However, he also highlights Noah’s materialism and preoccupation with wealth, beginning with his heavy taxations (v. 3, but especially vv. 8–14). This conjunction of religious/ economic problems had also plagued the Nephites during Jacob’s time (Jacob 2:12–13). Like Jacob, Mormon connects social and economic sins but definitely sees them as subcategories of religious sin, because religion encompasses all life. Both Jacob and Mormon saw an implicit association between sinful polygamy and sinful materialism.
“Whoredom” in the Book of Mormon is consistently linked either to riches (Mosiah 12:29; Alma 1:29–32; Hel. 3:14; Ether 8:16, 10:7) or to a more general category that includes contentions, strifes, and deceivings (Alma 30:18, 50:21–22; Hel. 6:22; 3 Ne. 16:10, 30:2; 4 Ne. 1:15–17; Morm. 8:31). After Helaman, the explicit connection between “whoredoms” and riches disappears, although many of the sins earlier associated with “whoredoms” continue to be mentioned.
Literature: Benjamin McGuire, a graduate student specializing in the ancient Near East and Old Testament, draws a parallel between the description of Noah as a wicked king and the Deuteronomic code for kings. He suggests that the phrase “… but he [Noah] did walk after the desires of his own heart. And he had many wives and concubines” is an intentional description of an evil king who violates the code found in Deuteronomy 17:17: “He must not take many wives, or his heart will be led astray. He must not accumulate large amounts of silver and gold.” He sees a similar oblique reference to Deuteronomy 17:17 in the description of Riplakish as a wicked king in Ether 10:5–7.