There's a serious issue here about whether or not this is indicative of the decline in people participating in civil society (Robert Putnam's book Bowling Alone is a worthwhile read on this) ie there's less public meeting places cos there's less demand for public meetings of all kinds, political or otherwise, or whether or not the internet has made routine face-to-face meetings like the ones commonplace on the far left redundant. That people are still getting involved in debates but online, not in person. Why participate in a choreographed meeting run by distant and shadowy forces when you can engage in a permanent conversation online for no effort in the comfort of your own home? Where you can drink and smoke without alienating anyone! Whilst wearing just your underwear, if you please. I bet there's people on this thread now who aren't even fully dressed and who are pissed/stoned and it's only 6:23pm! You can't get away with that a meeting.*
And if you're talking about pubs you could make a case for both of the above, not to mention the economic pressure of competition from nightclubs and cheap supermarket booze. Why go to the pub when you can get two bottles of wine for a tenner, go home to your empty lonely life, get smashed on your own whilst stalking your old school friends on facebook and drowning yourself in self-hatred?
* I once left a meeting early to pick up weed. I'm a very bad comrade.