https://stallman.org/discord.html

Discord is bad because it's a proprietary centralized silo platform that is hostile to third party clients. I also don't like how they redefine terms (e.g. referring to communities/groups as "servers" and emotes as "emoji" which is an annoying thing that has spread even to the fediverse). I don't like the culture of Discord and Discord-related memes/jokes.

The worst thing about Discord, however, is how so many communities more or less force it on users. I don't like Discord and would be a happier person if Discord disappeared off the face of the world tomorrow but I feel I am required to use it (with a libre third-party client) to participate in some communities and stay in touch with friends. But I use Discord as if it's a weird proprietary IRC-like thing, because that's all I'm interested in. I don't care for "emoji" or animated whatsits or voice chat.