Jose Iglesias is a defensively sound short-stop, but the Red Sox simply couldn't afford risking another hole in their lineup. They'll be breaking camp without Crawford, Cody Ross hit .240 last year, Saltalamacchia hit .235 in 2011 and is a career .244 hitter. So that's three holes in the lineup already. Also known as an easy inning.
Anyone who complains about the Sox "sacrificing defense for offense" is failing to see the larger picture that Iglesias would be hole #4 in that lineup.
And with the bottom of the rotation as shaky as it is, the Sox need to be able to have big innings and score runs in bunches. It can't just be Ellsbury-Pedroia-Youkilis-Gonzalez-Ortiz doing the production. There need to be hitters at the bottom of the order that can at least make an opposing pitcher work to get them out.
And if Iglesias is as great as some believe that he is, he'll do well enough in AAA to force his way onto the MLB roster. Playing time isn't given, it's earned.