for the cases where the culture is more-or-less universal
When is this ever true? The idea of a “universal culture” is exactly what I mean with this encouraging centralization. Even a specific community (subreddit) on a centralized service like Reddit will have a specific culture that is not in line with any “universal culture” (it’s likely to be skewed towards whatever culture exists in western english-speaking countries, just to mention an example).
I don’t see why not. Human culture is like a fractal after all :P. At least I don’t think we should discourage creating different places for the same topics, because different approaches is part of decentralization.