In the days when actual defense was allowed, rookie QBs were fresh meat to opposing defenders. I can remember we played the Eagles the year Randall Cunningham had gone down on opening day and was done for the season. They started a rookie QB and the Dome Patrol knocked him out the game by the third quarter.
All consternation with today's sport a given, there should be no reason on Earth a Saints team possibly playing for a #1 seed should lose to a rookie QB playing for a lame-duck coach. No reason on Earth.