Part of the issue may be disease also. Hogs around here, Arkansas, tend to have alot of diseased animals in the herd. I know of folks that kill them and leave them lay, never even walk up the them. Others catch them in a portable pen, kill every pig they catch, then move the pen to another location and do it again. It is done in an effort to get the animals off of their property.
I don't blame them for it. I have some friends that have pigs on their farms and lose major portions of crops and fields almost overnight when these critters move in.
Like RF said, questions like this need to be looked at through the eyes of the man making the decision. If they were hurting my crops, therefore hurting my income, therefore hurting my families wellbeing, I would do whatever it took to cure the problem. Regardless of what another thought was ethical.
I am not trying starting a base for arguments, but a person needs to know the whole situtation to make a judgemnt call. If it was just hunting situtations and the person simply had a low reguard for the pigs, then I would tend to agree with you.