The better question is why would we block big game trophies that are taken legally? Fees and licenses paid by hunters help preserve wild game.
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Part of the problem is determine whether or not what is coming in is “legal”. Corruption is rife. Once you start allowing animal parts in you encourage illegal killing and poaching and marketing of animals, most of whom are endangered. The Chinese are among the worst because they believe animal parts have medicinal or sexual enhancement property.
People who get their thrills killing these magnificent members of another nation should be satisfied with photographs and memories. We don’t need dismembered body parts brought back to encourage trade in those parts.