If the documents are confirmed as forgeries, then CBS obviously has no legitimate reason to protect their "sources". The public has a right to know EVERYTHING about how they came into possession of the docs. If CBS won't come clean, we need a UK-style investigation (BBC / Lord Hutton / http://news.bbc.co.uk/1/hi/uk_politics/3437315.stm/ ) to determine exactly how forgers attempted to use a major news network to influence an American presidential election.
CBS are not trying to protect their sources.
They are trying to protect themselves.
When and If it becomes obvious to Americans that CBS were in wholesale colusion with the DNC, or unknown sources hostile to the President, any cloak of objectivity will vanish.
It doesn't add to their credibility that they were so interested in destroying President Bush that they fell for such a transparent scam either.