Becuase MOAR PASS RUSH is needed.
The secondary isn't that bad. It's actually looking better than it has in a while with Chung, McCourty, Dowling, Bodden. Meriweather isn't a star but he's not as horrendous as some say. Butler and Wilhite could be decent slot guys. Arrington improved as the year went on but is a depth guy.
The Pats pass defense was absolutely awful last year. 30th in the league.
The Pats 3rd down defense was the worst in the league last year. That's 32nd in the league. They allowed opponents to convert nearly 50% of their 3rd down attempts.
The Pats defense could not touch the opposing team's QB. The pass rush has been subpar to bad from 2008 on.
You can talk about "scheming pass rush" all you want, but Belichick is not a creative blitzer like Rex Ryan or LeBeau, nor does he want to play that style. He wants to rush four guys and confuse opponents with coverages. To do that, you need better pass rushers than Ninko, Cunningham, Moore, Murrell. You need better DE/DT's than Brace, Deaderick, Pryor, etc. Maybe Cunningham steps up this year, but you still need another guy.
The last few years we have been asking ourselves, "Can the Pats win it all IN SPITE OF a Belichick-coached defense?" Did you ever think you'd live to see the day those words were uttered?
As Felger would say, the Patriots tried to and unfortunately have successfully become the Colts. Too reliant on Brady and the offense to outscore teams in a shootout fashion.