I can't speak about Dublin sessions but there is a habit among afficionados of Irish music that seems (to me) to be both unfortunate and widespread. Gulliver describes a version of it. In its more moderate expressions it allows participants to concentrate on technique and repertoire but in its more extreme manifestations it comes across as reactionary exclusivist and nasty.

That said, I've experienced pubs in Australia (mostly Canberra, at the time dominated by extreme middle classes) where singing was forbidden on the grounds that it started fights. But they invited our bush band to play regular gigs for a while, after which a session did get going for a few years.

And, when Ansett was still an airline, it used to be a common practice that folkies would gather at the train station or airport for a session to farewell one of their number who was leaving for any great length of time. There'd be long set dances down the station platform and lots of singing. At Canberra Airport, the TAA staff (I'm showing my age here) welcomed singing and music but the Ansett staff prohibited both. There was one celebrated Christmas where people had come from Melbourne and Sydney to sing carols in a major get-together. Afterwards, at the airport, we needed drinks (available from the bar) but the bat staff vetoed singing. We were allowed to sing outside the bar but not drink there. The bar door was in the TAA section so we compromised by standing outside the door, singing, while holding our drinks across the threshold in the bar area. We didn't interrupt customers, many of whom joined in the fun and, while it's not quite the type of session that started the thread, I though some of you may welcome discussion that (vaguely) centred on its topic.

Cheers, Rowan