The OP seemed to be speaking more broadly about any community being able to grow without ruin, and there are plenty of examples of communities that grew and improved in quality for arbitrary amounts of time. When we talk about online, fast growth, low-indoctrination, easy-to-join communities (i.e. they grow from without vs. within,) those are prone to the eternal September effect and to losing/changing identity. There are all sorts of circumstances that can effect a groups growth dynamic, like how hierarchical it is, how communications are prioritized and presented, etc.

I think fast growth and low barrier to entry are a recipe for becoming a microcosm of general human behavior/cooperation issues, but that there are mitigating factors that may allow it to work better or worse.