Continuing on the subject of publicly accessible Slack content, since the phrase "closed social network" has been come up, it's important to note that Slack's ToS is different from Facebook's (and Twitter's and LinkedIn's et al): when you post content to Facebook et al, you still own it -- Facebook et al just has a license to use it (a pretty extensive license); when you post content to Slack, you do not own it -- the company, organization, or individual who runs the workspace owns it. See https://slack.com/terms-of-service/user for more details.