You must remember that sometimes a lot of warnings and discipline happens in PM to protect the feelings of the brother or sister. I know of two people (not well known) who were banned for sending me and other members very nasty PMs. But on the regular board they weren't saying anything against the rules. I even had a member join, not post a single post, just to PM me some serious vitriol. (accusing me of being a Jewish spy, etc., etc.,)
maybe you are right. But look at the posts that were out in the open. Banning is one thing but to list someone as spammer so all their posts disappear, i don't see any reasoning behind it unless you have an agenda of some type of censorship. I"ve never seen any one on any forum to do this regardless of how bad the member became, only the nasty posts were deleted and the user banned.