You made many good points, but I'll take issue with this one:
> If you are having legitimate complaints about your job and you want to vent or validate your concerns before proceeding, you might want to have a private conversation with a coworker - and you might legitimately be afraid that your unfiltered, undiplomatic private conversation might be taken out of context or retaliated against.
If you were retaliated against for your legitimate complaints in private Slack conversations (via firing, harassment, etc) then the records could be subpoenaed for you to prove WHY you were being targeted.
> If you are having legitimate complaints about your job and you want to vent or validate your concerns before proceeding, you might want to have a private conversation with a coworker - and you might legitimately be afraid that your unfiltered, undiplomatic private conversation might be taken out of context or retaliated against.
If you were retaliated against for your legitimate complaints in private Slack conversations (via firing, harassment, etc) then the records could be subpoenaed for you to prove WHY you were being targeted.
It works both ways.