I don't like this trend either. What I particularly don't like is that to be signed in into multiple Slack communities, I need to add them to the Slack desktop app. And the more apps I have, the worse the desktop app seems to perform.
I wish the developer communities would realize that IRC has been around for years and performs much much better than Slack.
I wish the developer communities would realize that IRC has been around for years and performs much much better than Slack.