"I personally think having an "all-comers welcome" slot is a really valuable thing, and because it's always given it's own little box, nobody could possibly confuse it with "the real thing" - so I don't see how it's detrimental to folk or any other sort of music that indulges it."

Absolutely! It's no different than joining a watercolour class, chess club, hiking group, dinner party club or indeed any other sociable amateur hobbyists club.

Amateurs aren't considered representative of or responsible for the overall condition of any other art-form or discipline that I'm aware of?