Of course the problem with listening to the voice of the people is that the people might make a mistake, as Mosiah has allowed.
Mosiah exhorts his people to make choices in accord to the commandments of the Lord, and that in so doing they might find themselves always in the right. However, since the wrong might occur, he reminds them that the consequences of that wrong choice will be visited upon their heads. It will be just, because they will have made the decision.
This shifting of the responsibility from the king to the people might make people long for a king so that they do not have to shoulder the responsibility. Mosiah reminds them that having a king does not insulate them from the wrath of God. If there is an evil king, they also have the wrath of God poured out upon them, but then because of the king, not necessarily because of their own choices.
Mosiah is showing them a contrast here. While it is true that rights engender responsibility, having a king with that responsibility does not prevent the evils of the world from finding them, if the king is not righteous.