I've never been married, but did have a relationship destroyed this way. I was in your husband's position. With much perspective, I still feel as though she went beyond venting. A mutual friend told me the content and it was all one-sided story with commentary and advice that was based on that one-sided story. It wasn't helpful to her and obviously our relationship because the things she was saying should have been said to me so we could address it.
Not trying to judge, just sharing my own experience. People appreciate hearing the type of blunt criticisms that often end up in places like these before you put them out for the public to see. It isn't fair to the other person who may not understand the problems at hand.
That said I do understand the value of venting to outside folks. In my case it was hurtful because it was not anonymous so many things I assumed to be private were being expressed publicly without my knowledge, and I had not ability to rebut them.