I may be wrong in my assessment of the situation, but I believe a blind eye is used with regards to the posting of asshateous PMs, with an understanding that the anonymity of the offending asshat is maintained.
I get the impression that these types of PMs are sent:
1) By a handful of known, regular mouth-breathers, easily identified by their poor manners, mistreatment of the english language, proclivity to send the same message to multiple people, and vast collection of smart phone pics of their own peni, which they are only more than happy to send and share with strangers.
2) By new registrants, with a dick-pic collection to rival the experienced asshat, and as phlegmy with exhalations as his counterpart. Easily identified by a low to no post count, and usually as adept with words and punctuation as the seasoned (yet no better versed) asshat mentioned above.
Both probably have a copy & paste file as well, where they store their work and the work of others they've stolen from, for later (and repeated) PM distribution.
I hope your inquiry does not "wake the giant" and bring about enforcement. I, and I think others, enjoy reading the shared asshat PMs and the replies to them. I would imagine the only ones who would complain are the asshats themselves.
A thread of PMs from asshats is far more enjoyable and beneficial to others than a thread of names of alleged asshats. Knowing their names won't change things - they just change their names anyway.
And regardless of the names used, when I read these inappropriate PMs I envision the writers in front of their computer like this.