This is a commonly used parenting technique. Here, Nephi uses it on his brothers and new traveling companions. It is the old, "go ahead! Try it and see!" argument. When a whining teenager lacks the wisdom to see the consequences of a given action, a parent might try this argument. It does two things, 1) places the responsibility for the action in the court of the complainer, and 2) allows the complainer to learn by sad experience the consequences of their decisions. At any rate, the complaining promptly stops because permission for the action has been conditionally granted. Nephi makes it clear to the rebellious—there are going to be consequences if you return to Jerusalem; remember the words which I speak unto you, that if ye go ye will also perish; for thus the Spirit of the Lord constraineth me. Unfortunately for Nephi, their response was more rebellious than that of the average teenager—they decided to kill him.