Even though it requires the illegal alien's 100 days of agricultural work in the U.S. to have occurred during any 12 month period between February 2002 and August 2003 - and, therefore, is not something new "invaders" could cash in on - this legislation further reinforces the expectation that, if you can get into this country by whatever means, you will at some point likely be allowed to stay legally.
Gut flora were once thought to be harmless residents of the guts of mammals, and in time it became clear that they not only aid in digestion but also protect against the arrival of more harmful invaders.