Email:

- multiple clients on multiple platforms

- multiple clients on emacs (e.g. Gnus, mu4e, NotMuch)

- does not require a browser, ever

- does not require executing untrusted code on my computer, ever

- open protocols

- multiple servers on multiple platforms

- federated

Github, Slack et. al.:

- may have a decent text-only client (e.g. there's a Slack mode for emacs, and there are some GitHub clients out there, which may or may not be convenient)

- strongly encourage and sometimes mandate use of a browser with execution of untrusted code allowed

- protocols controlled by a single organisation, with no possibility to add functionality on the server side

- servers controlled by a single organisation

- no federation

- fundamentally proprietary

What I value: freedom; TUI clients; emacs clients; open protocols; being able to run my own service.

You listed only positives for Email and only negatives for Github etc. but you implicitly made the claim that decentralization and freedom are more valuable than all of slack and Github's features combined. Or are you saying that the value of everything except your "what I value" list is zero, so all of github/slack's objectively useful features are weighted to zero in the calculation?

> you implicitly made the claim that decentralization and freedom are more valuable than all of slack and Github's features combined.

I can't speak for others here, but personally I treat freedom as my first priority: it doesn't matter what features a platform offers if it doesn't offer freedom, because I will not use it if it doesn't offer freedom, therefore I'll never see any of those purported features.