The comparison being that several hundred years ago if you wanted to work in a certain city sometimes there would literally be one company that ran everything.

They were aptly named company towns:

https://en.wikipedia.org/wiki/Company_town#United_States

They have an interesting, and often sordid, history.

I know the history. The connection to slack channels seems absurd.

It's no different than companies stopping workers from organizing. It's scare tactics plain and simple. Rather than confront people and give real answers they take their ball and go home.

It's a poor look.