A reader has a more straightforward response to the question:
Pigs will eat anything, including human feces. In South American villages without sanitation removal and indoor plumbing, pigs are used to keep the area free of garbage and feces. Villagers sell the scavenger pork to cities rather than eat it themselves. Pigs also lack sweat glands and slop around in mud to keep cool. Thus pigs are considered unclean, similar to shellfish, which are also scavengers.
Another writes:
Jews don't eat pork for the same reason Muslims don't: trichinosis. Only they didn't know it was trichinosis. They thought it was a curse from God. Soliders got sick before battle from eating raw or undercooked pork (pigs and goats being a good food source for traveling armies because they were low maintenance and can/will eat anything). Sick soliders make bad warriors, hence the edict from on high to stop eating pork.
Another:
Hitchens' theory is nice, but I'm afraid it's probably incorrect. The correct answer, it turns out, is that Jews don't eat pork because pigs are not antelope.
Most contemporary scholars think that Mary Douglas cracked the purity codes of the ancient Israelis. Douglas was an anthropologist and specialized in understanding different cultures' understanding of purity. Her book Purity and Danger: An Analysis of the Concepts of Pollution and Taboo is a classic on the subject. She theorized that every culture divides up the universe based on a unique logic. But no matter what categories you come up with there will always be entities that defy them, things that are left over and unaccounted for or that violate the boundaries of the nice neat categories we've set up. It's these things that we call "impure." She writes, for example, in the context of the purity laws in the book of Leviticus that, "swarming things are neither fish, flesh nor fowl. Eels and worms inhabit water, though not as fish; reptiles go on dry land, though not as quadrupeds; some insects fly, though not as birds. There is no order in them. … If penguins lived in the Near East I would expect them to be ruled unclean as wingless birds."
When it comes to livestock, the cow served as the governing norm for the ancient Israelis; it 1) chews the cut and 2) has cloven feet. All animals that are like the cow in those two respects are clean, but animals that chew the cud (or at least appear to) but don't have cloven feet, as well as animals like pigs who do have cloven feet but don't chew the cud are rendered unclean and therefore unfit to eat. Here is her conclusion on the matter in Purity and Danger:
Note that this failure to conform to the two necessary critiera for defining cattle is the only reason given in the Old Testament for avoiding the pig; nothing whatever is said about its dirty scavenging habits. As the pig does not yield milk, hide nor wool, there is no other reason for keeping it except for its flesh. And if the Israelites did not keep pig they would not be familiar with its habits. I suggest that originally the sole reason for its being counted as unclean is its failure as a wild boar to get into the antelope class, and that in this it is on the same footing as the camel and the hyrax, exactly as it is stated in the book.
Another:
Gordon Grice makes a strong argument in his book The Red Hourglass: Lives of the Predators that pigs may be routinely shunned as food by desert cultures because they are notoriously good at rooting corpses out of the loose and arid soil. (Sealing a body in a stone tomb/cave ala Lazarus had a practical purpose after all.) Thus eating the flesh of a pig, especially a wild boar, may indirectly result in cannibalism.
Another:
Reading this post reminded me of a scene from an HBO documentary I'd seen several years ago. The documentary was about serial killers and cannibals in particular. I do not remember the name of the documentary but the women that was interviewing a man that was jailed for murder and cannibalism in the USA asked him what eating human flesh tasted like. The reason this sticks in my memory is because of his response to her query. He looked her in the eye and thought for a moment, then said, "You would taste like the best ham you've ever had."
Creepy.
(Photo by Flickr user red hand records)
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