It's very, very hard to go undefeated in the NFL. If the Pats go undefeated, you can't simply say, oh, they had a sh*t schedule. A few things go wrong in a game and it's very easy to lose. No sh*t team wants to lose. They want nothing more than to knock off the Patriots.
Fact:
Apart from the 1972 Dolphins, three NFL teams have completed undefeated and untied regular seasons: the 1934 Chicago Bears, the 1942 Chicago Bears, and the 2007 New England Patriots.