I'm not sure this is your position, but one extreme is to describe this "shared reality" as being imposed by force on everyone by one privileged group.
But I'd like to highlight other forces. One was technological, 3 TV channels or whatever was all they could do, and this implied that there was going to be a pretty high degree of conformity. You couldn't broadcast weird Italian movies because only a few percent were interested. The 4 big car companies who bought the ads which paid the bills really didn't want to be associated with anything partisan, they all needed to sell to everyone.
Another was historical / emotional. The nation had just emerged from this gigantic world war, and it was a spectacular victory, which gave enormous prestige to the huge centralized machines built to fight it. They built a lot of similar machines back home, big corporations with a commander-in-chief who wasn't a self-made robber barron, he was promoted up the ranks. Big unions, and big regulation.
This experience also squashed a lot of earlier differences. You say "Women? Marginalised people?" but this seems like a modern take, I think they would have said "Irish? Polish? Jewish?". These earlier identities and divisions were eroding in favor of this shared one, I mean, a Catholic could be elected president, that was a big deal.
But all of these are gone now. So perhaps 100 years ago is a better guide than 50 years ago.