A lot of my CEO and founder friends talk about this"... rephrased: "My CEO and founder friends are upset that their employees use a piece of software to talk about the toxic culture my CEO and founder friends have cultivated"
At most other companies I’ve had people message me about salary concerns, unionization, anger towards a manager or CEO, endless banter about anything but work, etc. The main difference was that these places were run by people who really didn’t care about their employees and slack ended up a reflection of that. A lot of upset, frustrated, resentful venting in private channels.
If slack didn’t exist, these conversations would have happened some other way. There’s no way everyone could keep sane in a bad work environment without some degree of venting or comradeship.
Having slack expose those faults in the management chain doesn't mean this is an employee/IC problem. These managers of the company should learn how to manage people better for $$$ they're (we're) getting paid for.