Do you know what kind of shitstorm would brew if he deleted the thread and banned him?

I don't see how it's different from calling out a former employer and spreading (what seems like) false information. Cruel and perhaps unprofessional, but not completely in the wrong imho.

I suspect you don't use Reddit.

Every time Reddit Admins delete a thread, it leads to a shitstorm.

EDIT:

If people publicly drag you through the mud, you have the right to respond.

> If people publicly drag you through the mud, you have the right to respond.

You always have the 'right' to comment about people, you always have legal liability in [anything resembling] an official statement.

If you make a demonstrably false statement, yes.

Simply because you shouldn't go around lying about people isn't really relevant tho...