It's been going one since the first companies tried to monopolize Internet chat by centralizing it on their infrastructure in the 90ies.

The argument for AOL/MSN etc back when the Internet was new openness for the unwashed masses just a dream is exactly the same being made by slack i.e. that by making it locked and taking away the complexity introduced by the existence of cross vendor compatibility new users face less confusion.

Well, this one was supposed to be a little different, as instead of open vs closed, it was sync vs async. But when the topic of OS projects and closed tools comes up...

and it needs to continue to happen until OSS communities ditch Slack.

You're never going to move large groups of people by just yelling "xxx is terrible!" You have to make something better that people want to use to get them to switch. Unfortunately, Slack is better than IRC in many ways that matter to a lot of people. Ignoring all of those things doesn't make IRC better, and it's not going to make people want to use IRC over Slack.

Because the things that are driving people to use Slack are the same as existed five months ago, and arguments like this do nothing to prevent people moving.