Even if I were to accept the premise that Rivera is not defending Cam enough (which I don't)
If Cam truly is fueled by the criticism why try to cut off that fuel supply?
Cam for all things is surely confident in his abilities. In some ways I think the criticism is good because it fuels desire and gives him humility and determination.
For example Michael Jordan was a guy that would just manufacture slights against him to fuel his insatiable competitive appetite. It gave him an edge
Rivera doesn't need to run out and defend Cam of every criticism against him. He needs Cam to come out every day with a burning desire to prove his critics wrong on the field.