Why do oppenents of illegal immigration continue to use sources/information that is debunked?

Question by Hotwater: Why do oppenents of illegal immigration continue to use sources/information that is debunked?
I’ve notice the claim below a few times, and other users try and help them by advising them that they are false claims, and opponents of illegal immigration continue to use them.

Is there a valid reason for this?
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Cost of Illegal Immigrants

Q: Do illegal immigrants cost $ 338.3 billion dollars a year? More than the Iraq war?

A: A chain e-mail that makes this claim is loaded with errors and misleading assertions. Published studies vary widely but put the cost to government at a small fraction of that total.

■The e-mail includes a link to a CIS report that contradicts some of the e-mail’s own claims. The report found that illegal immigrant welfare use “tends to be very low.” It also estimates the total federal net cost of households headed by illegal immigrants at under $ 10.4 billion, a small fraction of what this message claims.

■One “paper” that is cited is a non-peer-reviewed, non-scientific study that essentially fabricates a number for illegal immigrant criminals.

■Five of the links lead to transcripts of Lou Dobbs’ cable television show, which fulminates regularly against illegal immigration and is hardly a neutral source. Furthermore, in all instances, the e-mail then takes the original Dobbs reporting out of context.

http://www.factcheck.org/2009/04/cost-of-illegal-immigrants/

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