Uncle Dave, the nice thing about Judaism is you don't have to be Jewish to have an opinion, however, if you get two Jews together you'll get three opinions...and separate synagogues.
                     
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McGrath, it is way more detailed than what I wrote. If you want the details go to Leviticus. If you want the exegesis, or the scientific rationale, there are many sites that you'll find on the web.

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Kendall--because they can (many don't)? tradition? because they are observant of Jewish law? there's plenty to eat even without eating non-kosher foods? Take your pick, or give a reason of your own.

JotSC