Slack poses lots of security risks from IP leaks to mass monitoring. They also changed their terms of service recently. It's basically a US government data collection channel now and the person who creates the channel is responsible for what the members of that channel get up to.

For secure communications, you can use the chat features of vTorrent. Group chat within the client might be available, but I haven't checked it out.

For instance, if people start sharing torrent links in Slack the devs can be held responsible if they set-up the slack channel. At the moment, vTorrent is a client that can be used by anyone. Some might want to use it for illegally sharing torrents. The devs can't control that, even if they provide a mechanism to encourage people to pay rights holders for content. 

Remember, some of these guys are nutters and will try to hold anyone responsible for anything:



https://torrentfreak.com/movie-companies-want-to-hold-search-engines-liable-for-piracy-161106/