What if the pigs had been people? What if it was human beings who were trying to get out of the flood waters and they threatened the integrity of the levee? Would any means to stop them destroying the levee have been okay? I mean after all, what's killing a couple of people compared to saving a town?
Do you know for a fact that all other options were exhausted before this step was taken? Do you know for a fact that vets were consulted? That any measure was considered before they shot the pigs?
Since you seem to know so much about it, why not give us the details that we must be missing?
I am the user formerly known as MrsKey