But just like with IRC, it's all about the specific community you've joined, not the platform. You can definitely find good communities on discord.
How could it translate online where anonymity is like a shell protecting you from shame?
The internet really enables large groups and strangers to join those without any kind of social capital buy in to the community. I think one of our biggest mistakes in online communities was thinking you could just open the doors, invite thousands of people in, and expect that to go well. That doesn't go well in the real world when there are real world consequences. Any concert or protest or big sporting event always has bad eggs in it. Think soccer fan riots or protests turned sour or concerts with heaps of assault going on.
I think you're right in some sense it's just that the influences of social mechanisms are different online. Anonymity is often just psuedo-anonymity inside small online communities. People still don't want their online handle tarnished as they use that persona to be part of communities, and they would lose their social capital with that handle if it went south. But it's also possible for strangers with worthless handles to show up and be horrible with zero consequences.
Maybe we need a communication medium that requires technical skills to operate again.
The general chats are whatever, but having a collection of people who may respond to an LFG call is great for when I want a higher-quality batch of compatriots for the more 'hardcore' parts of the game. Plus, they have a bunch of pre-made voice pods that cap at a game's player limit, and have built support for direct-in-Discord lobby invitations.