It's a perfectly reasonable defense to a charge of mail fraud, for example. Or employing illegal aliens. "But they told me they had work visas, and they showe

It's a perfectly reasonable defense to a charge of mail fraud, for example. Or employing illegal aliens. "But they told me they had work visas, and they showed me what later turned out to be expertly-counterfeited visas!" Why shouldn't that get you off the hook, if true?