"Girl From the North Country" and "Scarborough Fair" are related, to some extent ("remember me to one who lives there"), but they are by no means identical in either melody, rythm, or chord structure, to say nothing of arrangement. They are two different songs with a some noticeable similarities in theme and structure. So what?

The folk tradition is filled with hundreds and hundreds of songs that resemble each other somewhat in melody or chord structure and which share certain memorable phrases or images. That's part of what makes the folk tradition what it is. We build on the past backlog of lyrics, tunes, musical structures, and styles. And that's good.

It only seems to bother certain people when Bob Dylan does it. I wonder why? ;-) Because he is who he is, that's why. He is the single most influential songwriter of the last 50 years, and that's what pisses those certain people off.