But when we went to a meetup in Rome, that was even worse -- the only people who came were foreigners. Thus a hypothesis: traditionally Catholic lands are not friendly to LW-style rationality.

It's more due to the fact that very few Italians (or southwestern Europeans generally) have fluent English. I mean, in my experience the average English teacher in Italy has worse English than the average bartender or policeman in Prague. I don't think religion wouldn't have a large effect, at least not around Rome (though it possibly would further south and east).

Have LW meetups been held in the Republic of Ireland (an English-speaking “traditionally Catholic land”)?