Walter P. Monson uses "descendants of Cain" to chide those who fail to warn their neighbor.
Walter P. Monson, Conference Report (October 1916): 79-80
I trust the time will never come when a Latter-day Saint will even entertain the thought, much less let the word pass his lips, that was uttered bv Cain when the Lord asked him, "Where is thy brother Abel," who said, "Am I my brother's keeper?" Such persons, I tell you, are descendants of Cain, if not literally they are in spirit, and we as Latter- day Saints, we who have been warned have been taught to warn our neighbors thus becoming our brother's keeper.