This article would've been better with some concrete examples, or a study, or really anything to back it out. "Slack can be used for bad things". Well, so can email, mailing lists, support forums, internal chat systems (jabber), etc.

Not even one example, just "A lot of my CEO and founder friends talk about this".

As with any tool, it's how you use it. Best implementations I have seen of Slack is when the rules are clear for the beginning. Maybe channels are meant to be public and private is an exception, or the opposite (everything private to avoid noise). And clear guidelines. And to be fair, the discussion is usually a reflection of the company culture that is already present: formal, informal, direct. The tool just facilitates it.