Not to mention that in a centralized system only a single entity has to be manipulated to turn over the data, whether it's through court orders, laws, extortion

Not to mention that in a centralized system only a single entity has to be manipulated to turn over the data, whether it's through court orders, laws, extortion, corruption (as e.g. happened with Skype), or a combination of the above. In a decentralized system, the job of the centralization has to be done by the people who want access to the data in the first place. Have to ring more bells, creates more people who know about the spying. A much harder job and there isn't any "easy" access to almost all data any more.