SSN's or credit card numbers are not morally questionable per se, but their
publication would be mischievous or even malicious. That's because there are people out there who would use the information to steal identities or credit, so there needs to be a third party who will abuse the publication for their own gain. As a side note, I wonder if the publication of such numbers would be actually illegal or simply the subject of a civil damages action?
So far, I can't see how publication of these diplomatic cables can be used for significant gain by third parties. There really aren't many surprises for anyone in that arena, but the hard evidence allows mainstream media to confirm what many or even most people already suspected.
Incidentally, that's an amazing aspect to the reporting of the leaks; no-one is denying or questioning the content. It's almost surreal to read an article that you
know is true without worrying about the quality of the journalist's research, their bias etc, not to mention some vested interest group or politician denying everything and claiming black is white.
However, it is true that they are publishing content that is moral or ethically questionable. It's just that that has nothing to do with Wikileaks, it's the nature of the content! From an ethically bankrupt governor of the Bank of England to a State Department directive for diplomats to steal personal identity details (is this somehow better than publishing SSN's?), there's questionable content aplenty. It seems to me however, that the third parties who can take advantage of the publication are the long-suffering citizens of the various countries involved.