Earlier quoted context omitted.
I'm thinking a huge part of the difference between Slack and IRC audiences has to do with the $340MM Slack has raised. If someone gave "IRC" a quarter of a billion dollars, the differences might not be so obvious.
If you gave "IRC" a quarter of a billion dollars, we'd have the world's most complex ncurses UI, and a security ACL system whose complexity would rival X509. And normal people would still use Slack, because Slack was able to make simple design decisions that benefit the overwhelming majority of users but piss off Unix nerds like us.
that's just the nature of the beast, x.509 is also very old- but old things should be fixed or replaced with better alternatives, slack just fixes a usability problem.. but trades all privacy and freedom for that.
Personally it's not enough, but google has a massive market share because normal people do not consider that their data or freedom has any worth.
at least google is pro-free market in the way that you can extract data out later and migrate, I don't see slack being able to offer that reasonably. (or their incentive to allow it)