Are you saying that organizations that care to keep secrets get left behind by those that don't?
That sounds kind of ridiculous.
Organizations that refuse to use Slack are at a disadvantage. When employees show up and realize there's no Slack, they start to analyze all other company decisions. How much effort could be saved just by using Slack? Those secrets had better be important to justify this loss.
There are alternatives. Rocket Chat is self-hosted, and maybe it's sufficient. But second-place software will always feel second-place.
If your reasoning is solely "We are a company, so we have secrets," that's justifiable only in narrow domains, like a security company.
For the rest, and especially at startups, the strategic risk of revealing your secrets to Slack is counterbalanced by the fact that Slack can't take advantage of those secrets without committing suicide. The moment everyone stops trusting Slack, that trust is gone forever.
In the meantime, Slack has been a faithful steward. What are the risks? An employee could go rogue and steal the data. An acquirer like Amazon could use the data maliciously. Slack could get hacked and the data could be made available publicly.
Of those, getting hacked is the only relevant concern. Employees are unlikely to end their careers by stealing data. But if Slack's data is ever stolen and made public, everyone will have egg on their face simultaneously. That means it's less likely to be a disaster for any individual organization.
Talent has a way of sniffing out incongruities like this. When an organizational mandate doesn't pass the bullshit test, opinionated talent will usually try to change the situation, or leave. And opinionated talent tends to be effective talent.
When effective talent leaves, better watch out. You might have suddenly become one of those organizations that find it impossible to attract top performers.
To put it plainly, who would want to work someplace that puts the company's quality of life over the employee's over something so trivial?
Of the startups that will eventually survive, even if all of them revealed all of their operational and strategic insights simultaneously, they're unlikely to die. Or even be slowed down, really. Most startups are working on ideas that seem bad. That's why startup investing is hard. Revealing your seemingly-bad strategies to the world won't change much. And if your idea seems good, you tend to be entrenched. It's unlikely some other company could form and steal it from under you before you can execute on it.
In all but a handful of domains, we're left with repellant pseudo-justifications for avoiding the one tool that everybody uses. Hopefully those secrets were very important!
If I hire you, and your concern is "why can't I use this one specific chat service", I hired the wrong fucking person.
I don't get the stance that this is "hype" or a "bandwagon" at all.
If this is just going to be a game of "let's list every feature Slack has bolted on to their chatroom" then I don't care to play.
My friend's company used Hipchat over Slack for precisely that reason - they're a security company, one you've likely heard of.