The 1830 typesetter accidentally replaced protect with preserve, the more common expression in the Book of Mormon. The 1908 RLDS edition restored the original verb protect to the RLDS text. Elsewhere there are six passages where the text specifically refers to “preserving people”:
The change of protect to preserve in verse 30 was probably influenced by the occurrence of preserve earlier in verse 21.
There is one other passage that refers to “protecting people”:
Thus there is no strong reason to argue that the occurrence of protect in Alma 2:30 (“to save and protect this people”) is incorrect. Note also that the phrase “save and preserve” is redundant, unlike “save and protect”.
Summary: Restore in Alma 2:30 the earliest attested reading “to save and protect this people”.