"the MC handed out song-books to the attendees, and then spent the evening telling them which songs they were going to sing, and leading the community singing." What's the problem with that if it's what some people want to do? If it's not the way people think 'folk music' should be don't regard it as folk music. Maybe wonder why people were doing that rather that participating in what you think 'folk music' is on that evening.

Ditto pub tunes sessions with a limited repertoire. If the landord is happy, the other customers don't mind (or even like it) simply put it outside the scope of your perception of a tunes session. It's quite nice to be able to go out and play tunes with some others in the local community and stand a chance of playing for most of the evening. And to go somewhere else on another evening for something more fluid.