If you notice serious problems with federated messaging, it's an entirely valid choice to abandon federation instead of trying to make federation work. There's no evidence that a system that's (a) federated, (b) open to everyone and (c) non-spammy is possible in the first place; maybe it is, but even more likely you have to choose two out of three at best.

I don't see anyone repeating this fallacy w/regards to email.

The only difference between email and federated IM is email started out (mostly) federated and IM systems started out (mostly) not.

Only inertia is what drives this skepticism of federation in IM.

Just as there is no technical reason GateKeeper couldn't succeed on iOS just as it does on macOS, there is no technical reason federation couldn't succeed in IM as it does with email.

Just perceptions have to change.

Why spend time building a federated system when nobody was using the last federated system?

Ultimately most users just don't care about federation. Them's the facts. That's why everyone takes PayPal and only nerds use bitcoin.

Slack vs IRC, too. Twitter vs GNU Social. I'm sure there are more.

Firstly not nobody. Secondly, how can you grow it if instead of moving it forward, they roll it back? That's the opposite of progress.

> Ultimately most users just don't care about federation. Them's the facts.

Not really. Everyone is annoyed by this issue. But there isn't much they can do. People need to register on N different services and use N different clients to communicate with users of those networks when they need to. Do you think they appreciate this mess or find it highly convenient? But they don't have any other option (except may be not communicating with some of them at all).

People care about convenience, not federation. Google Talk and Facebook Messenger both supported it for multiple years and the number of people who used it rounds to zero. This is where we ended up. There was time for it, just no demand.

Launch a terrific, convenient new email service that doesn't federate and watch how quickly users will choose federation over convenience.

They did, it's called Facebook.

Slack if you don't like that example.

Those are IM services.

That work asynchronously even when I'm not online, that I can check later, that have functionally replaced almost all of the communication that used to happen over email...

It's technically and functionally identical to non-federated email.

Slack doesn't replace email. That's a silly marketing slogan. Imagine for a moment if it really did. What if Slack became so popular that everyone stopped using email? That would be horrifying. You wouldn't be able to communicate with anyone without using Slack because it doesn't federate with any other service. Every website would have to integrate with Slack for user account registrations. Etc. Decentralized federated communications is the backbone of the internet. The fact that IM services have never broadly adopted federation dramatically cripples the potential of the medium with horrible fragmentation and balkanization.

...and yet, here we are, where most people who wish to contact me will send me a message on facebook before they'll send me an email.

It's not fragmentation if there is a single one that the whole planet uses.

You're assuming here that federation = progress. That's the source of the disagreement.

Federation is clearly progress. Balkanized non interoperaiblility is not.