Why not just change the channel?
Because CBS is just like a big pothole in the middle of the road, sure you can drive around it, but it's for the publics' safety that you fill it up and make the road new again.
That's like the credit card commercial. "Changing the channel on CBS, $100.... but getting Dan Rather fired... Priceless."
This is altering/forging military records in an attempt to unseat a sitting president.
I don't think CBS intentionally concocted fake documents. In their sheltered, group-think world, they convinced themselves the documents were real and ran with the story.