[logicallee]

If (my example) instead of people messaging each other on facebook, every single person needed to run a server (such as an IRC server) at home - no centralization at all. (If five people want to talk to each other, there are a total of 10 connections because 4+3+2+1 to fully connect every node with every other node). That would be an (extreme) example of decentralization, and obviously centralizing chat so I can just use a thin facebook/whatever app is hugely convenient. Likewise the blockchain is a joke, a single $200 pc can trivially do the work of the entire bitcoin network, trivially - if it were centralized. This second example also shows what is meant by control. So it's a balancing act.

[astrodust]

The internet is both centralized, we need to agree on protocols, coordinate address spaces, issue domain names, and decentralized, where elements of it can survive independent of the others if they're temporarily disconnected.

The Bitcoin blockchain is an example of something that's a complete contradiction: It's a highly distributed highly centralized system. There's only one Bitcoin block chain, and everything must be recorded there for it to be valid. If, for example, Iran is cut off from the greater internet then that means you can't use Bitcoin in Iran.

BitTorrent is a much better example: There's no central authority, it's truly distributed, and highly fault tolerant. If Iran was cut off for some reason, all the Iran-hosted seeds of any content would still work.

[logicallee]

I agree with everything you've written.