This is maddening. There MUST be a away to convert private to public. You can have some safety features, like members can opt in. members can opt out of their messages etc. But it is completely screwing us over to have groups that were improprerly or not. understanding the issue of private channels that have no need to be private. Now its impossible to share links between critical discussions.
Slack’s biggest problem is its nearly impossible to find or link stuff between channels. The private channel blockage of links makes it infuriatingly worse. We would have never made these channels private in the first place if we had realized it.