thing is, there are plenty of jazz open mics too. In London, the Jazz Cafe does one on Sunday afternoons, and there's quite a few around south London and east London.

It's essentially the same principle as floor spots: nobody is suggesting they will be as good as pro guests (though sometimes they are).

This floorspot or "good enough for folk" debate will run and run forever, but it really doesn't need to. 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.