@DogToots @Em0nM4stodon This is also segregation, separation, cliquism.
Also I believe many people would want a "global email database", and it's a question whether it's good to enforce people not to use what they want or need.
Decentralisation isn't necessarily segregation, see #matrix for example, where the view is consistently the same independent of what server you're on, and it's decentralised.