Because you don't necessarily need to involve the police every time you're trying to set an interpersonal boundary. Most people are well adjusted enough to change their behavior when you ask them to, and you don't need the threat of firing or jail to convince these people. You just need to ask them, nicely but assertively, to stop.

When you post to the mailing list it's obviously gone past the "assert-boundaries" point, because you tried that already. Nicely but assertively is a problem with unreasonable supervisors in an "at will" state and a weak labour market.

The mailing list isn't just for calling out your supervisors, and the article implies that the managers of the list do give people the chance to respond. It sounds less like a way to anonymously out inappropriate or offensive behavior and more like a way to give examples after the behavior has already been dealt with.

HR is not really intended to be the employee's friend or advocate. They work for the interests of the shareholders and management. It can be like reporting police corruption to the police -- not always a very effective course of action.

>Why is confidential material for public consumption?

If a person voluntarily and freely posts to the mailing list, (s)he is deciding that this is not confidential. Of course, if it identifies other people who did not consent, then you have a problem.