I’m talking here about liberalism more broadly understood as the political philosophy stressing liberty, individualism, pluralism and moral equality as first articulated by certain philosophers in the 18th century and then adopted, in part, by governments, largely in West, in the 19th century up until today. So this definitely includes, mostly, the era you’re talking about (which is why I just went back and added unions to my list — a gross oversight on my part). And you’re right that most people, unfortunately, and particularly in the United States, consider liberalism to be a philosophy of the left. The truth is liberalism is probably a spectrum running left to right. Though, I’d say, if one goes too far in either direction one is no longer a liberal.
I also don’t think these mediating institutions are sufficient to thwart an authoritarian state but they are, in my opinion, necessary. That’s probably one of the reasons why typically authoritarian governments make it so hard to form such associations or crack down on them entirely.
Finally, I’m actually working on a much longer piece on this topic. It’ll be published within the month hopefully. We can discuss it deeper then. I’d like that. I always enjoy reading your comments.