A selection of reasons why ArchiveTeam should never use Discord (except possibly as a way for people to report shutdowns to us):
<Frogging> [Discord is] a proprietary, centralized protocol with a ToS that explicitly disallows third-party clients
<Frogging> it's for-profit and likely to shut down or be sold off when it fails to make a profit, as all such services do eventually
<Frogging> It's also antithetical to ArchiveTeam because it has no data migration story
<JAA> And we'd be breaking their ToS in a kind of impressive number of ways.
<Frogging> Seriously, Discord can fuck off forever.
Summary of a discussion in #archiveteam-bs on hackint on 2020-07-21 (logs): every "upload" of content that you do not own the exclusive rights for (quotes, pictures, memes, etc.) is a violation of Discord's terms. This would include even things released under a permissive license (e.g. Creative Commons) or in the public domain.
Discord is staunchly anti-privacy and will lock you out of your account about it: https://wowana.me/blog/guess-im-done-with-discord.xht
(TODO: Make this into a nicer list.)