I honestly don't see the harm in registering and posting on another teams messageboard, whats the issue with that ? I've not made a habit of it - I'll often just "lurk" in the run-up or aftermath of a game. But I quite like seeing what other clubs fans are saying about their own team and ours...
So the ONLY type of interaction you feel we should have with fans of other clubs is one that involves abuse ?
I think most fans are well capable of holding intelligent conversation with rival fans about their respective clubs, face to face or on messageboards without it descending into inane...