As you state, plucking an apple for food is morally fine - few would disagree, and anyone who does is likely to get quite hungry quite quickly. Meanwhile, killing people for food is obviously wrong, yes? Morally abhorrent, in fact!

But there's a spectrum between those two extremes. To set a boundary, you need to determine the reasons why one is acceptable and the other is not. Maybe you intuitively draw the line right next to the apple, eating plant life only - no fish, crustaceans, shellfish - or maybe you draw the line adjacent to humans, contentedly eating tool-using, communicative, emotional, social, familial, intelligent gorillas without feeling guilt.

But what makes it abhorrent to eat a person, and acceptable to eat a plant? As Bentham wrote, Singer quoted, and the article cites, I would agree that it has something to do with the animal's capacity to suffer. One might add positive capacities for joy, or broader ecosystem health needs, or other questions of relative utility for the victim and the farmer, but the point remains: A pig is a remarkably human-like animal. Not as intelligent or as emotional as a human, perhaps, but it's far closer to a human than that shrink-wrapped package of hot dogs in the grocery aisle might lead you to believe.

What qualities does a human have that a pig or dog does not? What metrics can you use to measure those qualities, and how do you set a threshold for where it becomes moral or immoral? Identify those, and you'll have a much more solid argument for why killing a pig is moral.