But these community members aren't insulated entirely, ever. A new account is always provided the same front page experience, due to default subscriptions, and

But these community members aren't insulated entirely, ever. A new account is always provided the same front page experience, due to default subscriptions, and most Redditors only add subreddits to that front page, never removing any. Even if they curate to an extreme level, the Popular feed is always the same for everyone. You need to manually override that feed with RES filters to eliminate content. So I think it's valid to refer to "The Reddit Community", with some caution, because there is a familiarity with some of the same content, and an ability to relate in certain modes of thinking. The same way as "The Tokyo Community" generally familiar with Shibuya crossing, the local weather patterns, and behavioral expectations. There's significant standard deviation, but also a commonality that enables a stronger connection to other members of the platform / city.