Mormon’s emotion overpowers his ability to write coherently, and this passage consists of sentence fragments and disjointed lamentations, unusual for Mormon.
By judging the Nephites to be “without civilization,” Mormon is delivering a moral judgment against human sacrifice and eating human flesh. For Mormon, no one who is civilized would do such things; therefore, those who do are by definition uncivilized. This judgment is not a description of city/rural lifestyles or Lamanite political complexities. Nor is it drawn from the older Nephite description of Lamanites as wandering savages. Rather, this is a judgment based on their barbaric (opposite of civilized) practices.
However, for more than two centuries, there were no “-ites” (4 Ne. 1:17). Lamanites and Nephites alike (assuming that the terms had more than ceremonial designations) “were a civil and a delightsome people.” Therefore these now-depraved people had been part of the great gospel community. “Delightsome” is a Book of Mormon term for those who follow the gospel. (See commentary accompanying 2 Nephi 5:21 and 30:6.) Mormon is noting their fall from grace—and the distance of that fall.
He asks, “How can a people like this, whose delight is in so much abomination—” but cannot finish the thought. The implied ending is: “How can God allow such an atrocity?” Mormon is experiencing the shock of many who learned of the Holocaust during World War II or the genocide waged between hereditary tribal enemies right up to the present, as in, for example, Rwanda. For many, such terrible inhumanity leads them to doubt God’s existence. With a limited understanding of the nature of agency, but with hope in God’s love and mercy, they think God ought to have intervened. His inaction seems inexplicable.
Mormon’s reaction is similar; but his question is not why Yahweh does not intervene to compel order but rather, “How can we expect that God will stay his hand in judgment against us?” Here is where Mormon asks his “why” question. Rather than deny Yahweh, Mormon affirms God but wonders why Yahweh’s intervention does not simply destroy those who would use their agency in such a way. Mormon wonders why, given such failure of righteousness on all sides, Yahweh does not simply destroy everyone.