Because this statement is written in the scriptures, we are tempted to read it as history. Perhaps it might have applied to the Lamanites at one point, but this is a pretty typical statement about people who do not belong to the group defined as “us.” We are civilized. They are barbaric. In fact, the description of barbarian is itself a remnant of such us versus them thinking. The Greeks used barbarous to describe anyone who didn’t speak Greek. It is a word for outsiders, and the connotation of being less than us is intentional, even when it wasn’t strictly true.
Thus, Enos will also say of them, that the Lamanites “were led by their evil nature … [to] become wild, and ferocious, and a blood-thirsty people, full of idolatry and filthiness; feeding upon beasts of prey” (Enos 1:20). Feeding on beasts of prey is the opposite of the civilized and agricultural Nephites.
Mosiah 10:12 says that “They were a wild, and ferocious, and a blood-thirsty people.” In Alma 17:14 they are a “wild and a hardened and a ferocious people.” Helaman 3:16 notes that after Nephites mixed with the Lamanites, “they are no more called the Nephites, becoming wicked, and wild, and ferocious, yea, even becoming Lamanites.”
This is the definition of Nephite prejudice. It is not against how people look, but whether they are us or them. It is the most common prejudice of human history, and it is rarely related to actual observable behavior.
As the quintessential enemy, they will become a scourge to the Nephites. In good times, the Nephites will repent and remember Jehovah. Eventually, when the Nephites will no longer repent, this enemy will destroy them.