The 1905 LDS edition accidentally replaced unto with into; the subsequent 1911 LDS edition, set from the 1905 edition, followed this secondary reading, but the 1920 LDS edition restored the correct unto. Elsewhere the text has instances of only “lifted up unto X”:
The critical text will therefore maintain the preposition unto here in 3 Nephi 6:10.
Summary: Maintain in 3 Nephi 6:10 the preposition unto (“and some were lifted up unto pride and boastings”), the reading of the earliest textual sources; the use of unto in this expression is consistently supported by usage elsewhere in the text.