In previous bbq blog articles, I've written about some of the suspected dangers of imported beef from Canada and other countries. Here's some more articles for your consideration regarding beef, pork, and other foods:
Chinese rice protein
Imported feed ingredients fed to U.S. pork supply
I think all imported food or food made with imported ingredients should be labeled prominently to make consumers aware of the "imported" status. Then consumers can chose to buy it, or not buy it based on an informed decision. A more agressive food lableing law would allow consumers to vote with their checkbook.
Would you knowingly purchase imported beef, pork or chicken to feed your family if you knew it was "imported"?