"If you want all that, then don't run a session, run a rehearsal. Announce tunes beforehand so people can learn them and have the printed music ready so you can expound upon it.

By the way, how do you expect everybody to know every tune when there are 1800 (I think) tunes in O'Neill's Music of Ireland alone"

I think you miss the point.

Irish traditional music (which primarily is what I'm talking about here but I think applies to all trad) is traditionally transmitted from player to player by ear, not dots. The dots are NOT the music, but at best a guide and at worst a distraction. You will never play ITM properly if you never hear a variety of accomplished players in action, you can't learn it from the dots alone. It's absurd to expect people to know the entire canon of Irish tunes (let alone English, Scottish, Welsh, Breton etc etc too), but sessions are full of tune players that never refer to music - why would you expect accompanists too?

If you can't play or lilt a tune, then you don't know it and can't accompany it effectively. Tunes you don't know sit out and listen a couple of times through then join in if you've got the tune, or sit out and wait for one you know.

"People are not showing disrespect just because they are still learning."

Don't put words into my mouth. I'm still learning, probably play pretty badly but show respect to the music and my fellow players. I show deference to those that have learnt properly and encouragement to those just starting out and want to learn. I was (and will be in perpetuity) that learner, so I never discourage someone who wants to learn. However, some don't want to learn and want to sit and thrash or bang away regardless; great fun for them, in my mind a tad disrespectful to others. We all bugger it up now and then (last Friday it was more now than then for me) but that's a world away from simply not bothering to learn about what you're playing.