There are sessions and sessions, aren't there?
For the tunes-puctuated-by-the-odd-song type of session it's fair enough to expect talking during tunes and reasonable to expect some quiet for solo songs.

Last night I was in a session that was definitely a singaround - participants took their turn to sing or play. There were a few quiet listeners. There were one or two present who may have been listening some of the time, but that didn't stop them feeling free to engage in loud and drunken conversation for time to time and someone tried to shut them up. Unreasonable? I don't think so - the session was in (and pretty much filling) a side room and there was a large main bar where there was noise and talking and plenty of room.

If a session wants quiet it shouldn't be held in a one-room pub - pretty obvious really.

Anahata