With this line of reasoning you could say that when person A is caught looking at porn by person B, both should be fired because B happened to see the same porn over A's shoulder.
If you intercept porn and delete it, you're doing your job. If you retain it somewhere and go back to look at it, then you're just looking at porn, violating company rules.
I was kind of stranded in Mountain View unless they schlepped me back to the airport because I happened to be flat broke when they flew me out, so I just signed it, but I consider it laughably the craziest, most paranoid, least binding NDA I have ever signed.
Talk about Duress. ;)
"My acceptance of the previous terms requires the following company policy to be waived:
- Watching pornography at work is grounds for termination."