The occupants of one lifeboat don't necessarily have free access to occupancy of the other lifeboat...
Lost in the argument is the fact that not only did the Gretna police block pedestrian access into Gretna, but at the same time the New Orleans police were blocking pedestrian access into New Orleans. I remember several stories of "self-deployed" relief workers with food and water and several with boats being turned back from entering New Orleans.
This case is going to bounce around the courts for the next several years. If the Gretna PD did indeed fire over the heads of the people seeking refuge, I believe that there will be he(double hockey stricks) to pay.