While I agree that private messages should stay private, if someone sends me a message that is itself abusive, it is an abuse of the privacy aspect.
For this reason I have no qualms making public the things they say by posting it in a quote. I used discretion in my thinking in posting it. Not allowing me to post it only encourages further abuse of the private message system by these people.
Furthermore, I find it unacceptable that some people choose to use the private message system to fill up your mail box with bullshit. For example, this person's insults could have filled up my mail box so that I would have not received some important pooning info from others.