Long story short:
Discord isn't open source
it doesn't encrypt messages end-to-end
it doesn't allow self-hosting
it's funded by Time Warner
it collects user data like crazy
and it was founded by a guy whose previous company got sued for privacy violations (among other things).
From my article "How to Avoid Funding the American Deep State":
'Fortunately, there's Tox. Like the Signal protocol, Tox is open-source and offers end-to-end encryption. Plus, unlike the Signal protocol, it's peer-to-peer (meaning it doesn't rely on central servers). The "official" Tox messengers also don't require your phone number or access to your contacts.
Since currently none of these Tox messengers are available for all major operating systems, here's a video about the messenger Riot:
(Matrix, the protocol Riot is based on, is not peer-to-peer. And, for the first three years of its development [2014-2017], most of the core contributors worked for Amdocs, which was co-founded by Israeli billionaire Morris Kahn.)
Two more open-source messengers worth mentioning are RetroShare and Kontalk. RetroShare is peer-to-peer and, like Kontalk, available for Android, Linux, MacOS, and Windows.'