[clojureyoureyes]

> I don't need my text editor to send email

You don't, there's an MTA for that, but for composing mail, filtering mailbox, searching and other text-related tasks Emacs has much superior interface.

> be an IRC client

Messaging consists mostly of text editing, especially in IRC, which doesn't have fancy stuff like stickers, GIFs, videos.

> What difference does it make what programs do those things, as long as they work well and I can extend the functionality as needed?

A consistent, self-documenting, extendable interface.