One thing I don't like about this is that having your internal and external comms in the same channel presents a large risk of some user making a mistake inside

One thing I don't like about this is that having your internal and external comms in the same channel presents a large risk of some user making a mistake inside that channel and accidentally sharing internal information externally. I can't count the number of times I've seen people reply-all when they shouldn't have (and come very close myself), reply to the wrong chain, forward sensitive information that was shown way back at the beginning of a long chain. I remember one incredibly egregious case where my director and manager had a long, drawn out discussion about terminating one of my coworkers in an email thread. About how it really needed to be done, but the timing wasn't ideal because they needed her to wrap up an important client project, but she was kind of bad at her job, so maybe they should do it now, but there wasn't anyone to pick the project up so they agreed to wait a month and a half. Later on their conversation turned to some other things that were relevant to my work, and the director forwarded the whole chain to me and one other person on the team to "see the details in this chain." Of course we brought it to the boss' attention, but the damage was done, and my coworker and I couldn't un-know what we had read, nor could we say anything to our coworker. That was an incredibly uncomfortable and stressful 6 weeks sitting next to the woman every day who I knew was going to be fired soon and being unable to say anything. I've seen people reply-all griping about clients and get walked out of the building minutes later. Yes, I realize that the "where was that message? Email or slack (or whatever)?" is a legit problem that creates some friction. But for my money, reducing the risk of blunders like that far outweighs the problems it presents. I really really want isolated channels.