Agreed. This is more akin to evolution being stuck in a suboptimal (and perhaps a dead-end) local minima - but it is still natural selection as more pleasing features = survival on an individual scale.
The vast majority (outside HN) would still choose the network where their friends are conveniently already located over privacy concerns. Especially when those concerns involve pictures of their cats or other trivial personal information.
You're on to something here. Consequently, it seems to be in the best interest of the affluent class to maintain the status quo, as it supports and furthers the divide.