"Folk music as performed on the folk scene is usually very different from how it was originally performed."
Howard is probably right there, certainly that is true about dance. The way the dances of Jane Austen's day were performed back then / when they were first revival (only yesterday, or nearly 100 years ago depending on your viewpoint) / now at clubs full of pensioners / now at 'zesty' clubs are all very different, and a lot of people think the way they first learnt is the 'right' way.

My dislikes are mucked up tunes, but I like interesting arrangements (one man's meat...). I don't like singer-songwriters with guitars droning on in sessions. But there are exceptions. Hate guitarists who cant keep their fingers off the strings but noodle all the time. It annoys me when singers give the whole story away in the introduction - why bother singing it.
Likes - all the rest. Traditional singers and musicians like Martin Carthy and Alistair Anderson (or do I mean 'revival').