I’m a little surprised to hear you say that, having set up my family on Slack. As a user, you just see that there are posts in a channel, you click or tap it to read them, and you reply as desired. And, even if you do make a mistake, you don’t have to worry about it being seen by the world, plus you can easily delete or edit anything you do.
Personally, I find Facebook horribly confusing, especially when trying to get to groups I’m in, or find specific comments on posts. And of course, Facebook intentionally makes the privacy settings as difficult to find and understand as possible so they can gull users into revealing as much information as they can.