Foreign Policy lays out the case plain and simple. Of course it's not as much of a wedge issue and doesn't play on popular prejudices so its not as popular. But the fact is the entire illegal immigration debate is looking in the wrong direction.

Which aliens are the bigger threat? | FP Passport

Total Cost

Placing it at over 1,000 times the estimated cost of illegal immigrants. The US should be working with our NAFTA partners to keep these out of all of North America, since by the time it reaches the continent there is not much that can be done.

One remark: Potatoes are olso a foreign species in Europe ...

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Government is the great fiction through which everybody endeavors to live at the expense of everybody else

Claude Frédéric Bastiat

true along with a host of new world foods. However, cultivated crops tend to grow in farmland, and are specifically cultivated there, the invasive species/bacteria/etc. tend to take over all across the place. Foreign and Invasive are not the exact same thing.