I think your logic is quite a bit off, actually. When Porter and Greer were healthy and starting, they were a very effective duo. It allowed Sharper to rove the field and be there for the big interceptions. Harper's number was called a lot on blitzes and run support. Turnovers were created, because the defensive schemes were a lot more aggressive.

When Porter and Greer were injured, that left the Saints starting an untested rookie who had his good moments, but should really be regulated to a nickel or dime role, at best. The third best corner on the team, Randall Gay, was battling injuries of his own (hamstring, concussion). Mike McKenzie played well in an inspired first game back against the Pats, but regressed in later games. The cornerback depth was exposed, so linebackers were having to aid against the pass more, and Sharper and Harper were having to play out of position to make up for the deficiencies at corner. Blitzing decreased and this allowed the Saints to be picked apart on the pass and bowled over on the run. As I posted in another thread, the return of both Porter and Greer in the secondary is going to be a major factor in the Saints' defense returning to their early season form.

I understand your concern, because the defense did look pretty horrendous in the last several games after the Patriots game. However, I think we may all be in for a pleasant surprise this Saturday. Look for Gregg Williams to unleash the hounds and put constant pressure on Kurt Warner the majority of the game.