My recommended settings for setting up a slack that you plan to allow public access to. Methods for adding public users include third-party utilities like slackin (https://github.com/emedvedev/slackin-extended) which enable active user badges, or simpler methods such as using the Share Invite Link
from slack itself.
If you only do two things, make it these two:
Make sure to disable all app integrations. There's a bunch that aren't secure for public slacks. Either deny all, or require review by an admin:
https://YOURSLACK.slack.com/apps/manage/permissions
Second, disable email in the profile view:
https://binaryninja.slack.com/admin/settings#display_email_addresses
The reset are optional settings that may or may not be required depending on the slack: