I saw the sequences leading up to the attack on the Helicarrier as Loki using his power, through the spear, to pit the Avengers against each other and make them much easier for him to take out-if they didn't take care of that for him. Getting them to stop and think for a moment, without Loki's influence was important, particularly for Rogers and Stark; Thor and Banner had their own "focus" moments, but the two Avengers who could lead a team needed to snap out of their depression over being manipulated by Loki (and acting like asses to each other), and Fury's little bit of theater served that purpose.