Feeding shit and trash to pigs, and other animals like chickens or rabbits, used to be a common custom in European countries as well. It's not as terrible as it sounds, since for the most time these animals don't get infected by human germs, effectively acting as a kind of walking antibiotic bag, and therefore it's an acceptable way of disposing of residues and getting some extra food at the same time.

A Jewish friend once commented that it's the reason for kosher laws. I'm not sure if he was trying to justify an ancient custom with modern insights.

As far as I know, it is the primary reason why pork is outlawed in Islam. But man, I didn't know it was as bad as that haha :P