Let's suppose you have 20,000 people gathered in a stadium for temporary shelter. You know that they cannot go back to their homes, and you know that they will not be there for more than 2-3 days.
Doesn't it make sense to spend part of the time that they're there getting them registered, attending to their needs with food, water, medical care, communications with remote family, and providing money to them so that they'll be able to purchase items when they leave?
What should have happened, IMO, was the paperwork and distribution of items should have been taken care of within 12 hours, and as soon as the storm cleared the people should have been bussed out of the city to other shelters. Instead they were trapped there, apparently due to bureaucratic bumbling bordering on the criminal.
Yes, they didn't need money in a stadium. But they would need money very soon after they left. Whether the debit cards were pased out at the Superdome or convention center or Astrodome doesn't really matter. (Though conditions were so bad in NO that it probably didn't make sense to do the distribution there - there probably would have been even more crime had it happened there.)
The N.O. stadiums were intended for temporary shelter during the storm - not to be a giant tent for people to live in for nearly a week. After a couple of days, keeping people there was more dangerous than having them walk out of town.