The common issue for all of the services are when they become mainstream. It attracts bad apples. Twitter used to be and still have some great interactions just like small subreddits do, but when a post reaches /r/all or the feed of a controversial celebrity, you know it's going to be awful.

Discord is more like IRC used to be. It thrives in small communities of 30-50 people where you talk regularly and each topic has its own channel so regular chitchat doesn't drown out the interesting bits. It's more of a daily pub talk with your friends than finding a tutorial 10 years after it was written.