I take the point made by Mysha that unless variants are allowed to stand there cannot be the refining folk process which gives us some of our most iconic songs.

Unfortunately I cannot agree that "people are unlikely to tinker with an understandable text" - far from it. The examples given show how well-crafted meaningful words sometimes get mangled by the tin-eared into something less lovely, and frequently with a different (or no) meaning.

It is a problem which has no solution that I can see. We can but try to look at what appears to be the source, and to judge well whether a particular variation adds to the song, or detracts from it. The urge to alter should be balanced by the careful reading of the original to check that it is not our own comprehension that needs improvement.