Field position arguments not withstanding (see below), special teams AKA "The Kamikaze Squad" has got to be, almost without argument, play for play, the most dangerous one on the field.
Others can debate coaching philosophies all they want, but every intelligent coach recognizes this. I mean c'mon, this is the primary reason we don't see many front line running backs or wide receivers bringing back many kicks or punts. And before you mention the rare exception, they are USUALLY extreme cases where a RARE exceptional return talent, in the eyes of the coach, who knows the injury risks, determines that his field position advantage is worth it. And to top it off, even in this situation, I would wager that this coach internally evaluates this players use almost on a game-by-game or even play-by-play basis.
Heck, as a fan I like/liked seeing Welker and Edelman make returns. But as a coach, not so sure. It's not like they are breaking for TD's every 5 or 6 games, are they? So how much is an assumed advantage of 2-4 yards a return versus the increased risk of injury worth to the Patriots? Only BB makes that call.