Teaching "after this manner" can indicate that there are many who teach this philosophy. It can also mean that there are many who teach some version of this philosophy. This second is more likely, because the extreme statement that Nephi gives may be too obviously incorrect for some to believe. However, variations on this theme that have the same effect but address some of the effects of sin have a tremendous opportunity to influence the world.
Literary: Nephi restates Isaiah 29:15 in this context:
Isa. 29:15
15 Woe unto them that seek deep to hide their counsel from the LORD, and their works are in the dark, and they say, Who seeth us? and who knoweth us?
His use of Isaiah here is no longer the pesher-style commentary, but a literary usage which uses phrases from the known text to ground his discussion in a known text. This is the artistic device similar to the jazz performer quoting a famous piece in the middle of another tune. Nephi is using Isaiah as an artistic reference here rather than as a proof text or commentary on the text.