Thanks Jeff. It appears that as a new user of slack, I was less familiar with their open and closed channels and it was more likely that I was creating open channels there, and not private ones.

That said, after having made this mistake, (on both sites), I can still see the desire to make a public group private should the content head in a direction that justifies securing it, and vice versa in the case where a team wants to be transparent about the genesis of a project that has been in the works privately for a while.

Totally agree with the OP. Just migrated in my channels from slack and they all showed up as public forums, and they should be private teams. Ideally, I would just like to change a setting from public to private, (and/or vice versa), assuming that both types work in nearly the same way.