I was going to give it a rest. Really. But I couldn't overcome my bad
habits. They outnumber me ten to one ;-)

Plan 9's aptitude for becoming easily distributed--that is, becoming
decentralized--gives rise to a centralized system when it comes to
security, because safekeeping of one auth server is much easier than
keeping track of numerous authentications/authorization databases spread
across the network.

It's good. For a _large_ organization, it's good. For the same reasons
time-sharing systems were good for university campuses. Centralization
lowers overhead--in costs, time, security, and general maintenance hassles.
Problem is, sometimes the center and the periphery are the _same_, e.g. in
home computing. And for the same reasons a time-sharing system would be bad
for home computing, an innately distributed system is also bad for it.
Needless to say, home computing doesn't mean casual or insignificant
computing. The term only denotes the individual--to contrast with
organizational--quality of the computation involved.