A lot of these arguments read intuitively, but: Federation has the problem of being harder to prevent abuse. But this is also an issue with centralized system

A lot of these arguments read intuitively, but: Federation has the problem of being harder to prevent abuse. But this is also an issue with centralized systems (see Facebook, Twitter right now). And for systems that use the phone number as the user's identifier, like WhatsApp or Signal, it's even harder: which server is associated to an user? What to do if the user registers to more than one server? How to prevent a server from saying it has registered a user, when the user didn't do it? This is "hard", but solved. Bitcoin and similar systems do this (prove identity) very well already. And when you control the whole infrastructure, it's easier to provide a good user experience. With federation, you are depending on the quality of other's implementations. Google doesn't control email, gmail is still a pretty good experience. Controlling the infrastructure should lead to better quality and experience, but practically often doesn't. Does anyone love iTunes?