The City Journal article about porch pirates was interesting, but I think it misses an important piece of why it bothers us so much.
We want to live in a certain type of place. We want to live in a place where we don't have to lock our doors, where we hope people will keep half an eye on our place while we are away. People who violate that are taking more than a delivery of a cute coffee mug or a few shirts on sale. While they are not breaking and entering, are not actually invading our homes, they are invading our property, our space. They are not just taking something from our bank accounts, but from our lives. Thieves stealing our stuff from the warehouse on its way here would be an irritation, not an infuriation.
We regard it as a crime against our community, and we would also be upset if a neighbor's items were stolen, more than we would if the neighbor's goods were stolen from his car while he was shopping at the mall.