As noted earlier, it is unlikely that such a major shift in worldview would happen in such a short time. Mormon has foreshortened the tensions into a more black and white picture of righteousness and wickedness rather than describe the complex interactions that were surely part of the social fabric at this time.
Mormon had a people who were almost all righteous after the signs of the birth of the Messiah. From the standpoint of religious history, he could have had nothing else. Of course the birth of the Messiah was powerful and convincing. Now, however, we have a nearly universal apostasy from that time of belief. At this point Mormon is setting the scene for the destructiveness that comes with the Atoning Messiah arrives. The arrival of the Messiah is supposed to destroy the wicked. This is a theme well-known in Biblical literature:
Psalms 101:6-8
6 Mine eyes shall be upon the faithful of the land, that they may dwell with me: he that walketh in a perfect way, he shall serve me.
7 He that worketh deceit shall not dwell within my house: he that telleth lies shall not tarry in my sight.
8 I will early destroy all the wicked of the land; that I may cut off all wicked doers from the city of the LORD.
The Psalmist understands that the coming of the Lord will bring destruction for the wicked and favor to the righteous. In the New Testament, this theme is even more powerfully presented:
Matthew 13:36-43
36 Then Jesus sent the multitude away, and went into the house: and his disciples came unto him, saying, Declare unto us the parable of the tares of the field.
37 He answered and said unto them, He that soweth the good seed is the Son of man;
38 The field is the world; the good seed are the children of the kingdom; but the tares are the children of the wicked one;
39 The enemy that sowed them is the devil; the harvest is the end of the world; and the reapers are the angels.
40 As therefore the tares are gathered and burned in the fire; so shall it be in the end of this world.
41 The Son of man shall send forth his angels, and they shall gather out of his kingdom all things that offend, and them which do iniquity;
42 And shall cast them into a furnace of fire: there shall be wailing and gnashing of teeth.
43 Then shall the righteous shine forth as the sun in the kingdom of their Father. Who hath ears to hear, let him hear.
Mormon is setting up the scene for just such a winnowing judgment. Even the burning with the fire will be part of the fate of the wicked of the land. The destruction is coming, and Mormon presages it with the widespread wickedness that will be destroyed.