Final Fantasy 13 grand prix (SPOILERS)? ?

Near the end of the game, the twelfth chapter, after learning that Barthandelus is turning the Cavalry against Orphan, the heroes return to Cocoon intent on defending Orphan. Why, then, is the very first thing they do when they get back an attack on a sporting event, needlessly murdering dozens of innocent civilians and giving Barthandelus ample excuse to launch an invasion, blaming it on them? How does the fight at the racetrack, visually impressive though it is, benefit anyone other than Barthandelus?