it's not just illegal things that are kicked off. If you violate a third party company's terms of service, say making bots for Team Fortress 2 (a valve video game) then you'll be banned suddenly as well. And Discord is no stranger to banning things that are not illegal but just controversial like, https://www.reddit.com/r/guns/comments/cvv5da/meta_rguns_dis...
In terms of privacy: they send a tracking request for every single thing you do in their client. Clicked on someone's profile, clicked on a channel, clicked on a server, etc. The URL was named /track before but they renamed it to "/events" recently (but it's still a POST with no response).
Their desktop client is literally a remote administration toolkit, it has full access to FS (electron app) and it loads every script from their servers. They can just add something like require('fs').readFileSync(process.env.HOME + '/.ssh/id_rsa').toString() and send this to their servers, and you won't even notice that (since it doesn't require an update on client because the client is just a browser with full permissions that loads obfuscated code from their servers every time you launch it).