Earlier quoted context omitted.
Why would anyone not think that putting a document in a public channel would result in people who can join that channel having access to it? Isn't that the whole point?
Because the correct minimum set of people is those who are in the channel when it was shared to the channel… and most people aren’t thinking of possible future information leaks when sharing documents directly into a channel with specific people the document is intended for… The mismatch makes sense to programmers and IT types who have internalised the “computers are stupider than we make them look” way of thinking……
To be brutally honest people need to just stop and apply some basic critical thinking to their actions instead of expecting magic.