Now I say unto you let us be wise and consider these things, for we have no right to destroy my son, neither should we have any right to destroy another if he should be appointed in his stead.
What does Mosiah mean, “destroy his son”? How would being king destroy him? Well, read the previous verse:
… I fear there would rise contentions among you. And who knoweth but what my son, to whom the kingdom doth belong, should turn to be angry and draw away a part of this people after him, which would cause wars and contentions among you, which would be the cause of shedding much blood and perverting the way of the Lord, yea, and destroy the souls of many people
So, it’s not destroying his son’s body he’s worried about, but his soul. If the people go wicked, and he goes wicked again as well, then his soul would be destroyed by his wickedness.
That’s why they had judges instead of kings:
Therefore I will be your king the remainder of my days; nevertheless, let us appoint judges, to judge this people according to our law; and we will newly arrange the affairs of this people, for we will appoint wise men to be judges, that will judge this people according to the commandments of God.
But what if the judges go wicked? Well, then the judges would be judged:
And now if ye have judges, and they do not judge you according to the law which has been given, ye can cause that they may be judged of a higher judge.
If your higher judges do not judge righteous judgments, ye shall cause that a small number of your lower judges should be gathered together, and they shall judge your higher judges, according to the voice of the people.
And maybe then, the wicked judge might remember righteousness.