Quite apart from following after the “lusts” of his eyes (Alma 39:9), Alma is concerned with Corianton’s doctrinal apostasy, which he phrases in terms of being “led away.” In addition to warning him against “any vain or foolish thing,” he specifically warns him against “those wicked harlots.” Earlier, in Alma 39:3, only one harlot, Isabel, was named. Here there are “harlots.” As I read this passage, “those wicked harlots” refer, metaphorically, to “any vain or foolish thing.” Perhaps Alma is associating “harlot” with the general conception of the apostate church, following 1 Nephi 13:7–8:
And I also saw gold, and silver, and silks, and scarlets, and fine-twined linen, and all manner of precious clothing; and I saw many harlots.
And the angel spake unto me, saying: Behold the gold, and the silver, and the silks, and the scarlets, and the fine-twined linen, and the precious clothing, and the harlots, are the desires of this great and abominable church.
Alma may be associating Isabel, a specific harlot, with the more serious religious “harlots,” meaning the false beliefs of great and abominable church. I hypothesize, therefore, that Alma is telling Corianton to avoid in every way the church of the devil.
Alma concludes this verse by naming yet another sin that compounds Corianton’s original sin: causing unbelief in others because of his bad example. We are all aware of how a misbehaving Church member can make it difficult to teach the gospel to others. Alma’s inability to assure his son’s orthodoxy was seen as a weakness in the doctrine, not as rebelliousness in the person of Corianton. The Zoramites used Corianton’s misbehavior as an excuse for not believing Alma.