". . . that beginners in traditional music will come to no harm if they learn tunes from books—"

What "harm" can they come to? I know plenty of people who learned their first folk songs from song books, then went on to be fine singers of traditional material.

No. To try to discourage a beginner from learning songs from written music is doing them a great disservice. There is absolutely nothing "harmful" about learning traditional songs from written music. Especially if they have access to hearing traditional music, it will do them no harm whatsoever, and it will provide them with a valuable resource for learning songs.

There are no sharks in the bathtub!!

Don Firth