Key Points:

The debate over reforming immigration law, pushed by President George W. Bush but blocked in Congress, was clouded by a storm of rhetoric from both sides that fudged the facts and confused the issues.

Do undocumented immigrants steal jobs from native-born workers or simply fill the jobs Americans can't or won't do? Is their presence a drain on the health and social security system, or do they contribute more to the economy in taxes than they take out?

These sound like simple enough questions to settle, but the shrill national and local debate - fuelled sometimes by presidential campaign politics and sometimes by deep-seated prejudice - made it hard to pin down the facts.

"This country absolutely needs a robust debate on immigration [but] public debate has become rancid on this topic," said Mark Potok, director of the Southern Poverty Law Centre's Intelligence Project.

"It has become degraded to slinging a bunch of false accusations back and forth."

In recent months, Americans have been bombarded with often contradictory and highly charged arguments purporting to prove undocumented immigrants are either a boon or a bane for the economy and society. Analysts say public understanding of the issues is clouded by reports put together by partisan think-tanks and lobbyists, as well as by accounts from "advocacy" journalists and talk show hosts and in the free-wheeling exchanges of blogs.

Many opponents claimed that illegal immigrants take jobs from US-born workers.

Employers from Arizona to Texas shot back that thousands of farm, construction and restaurant jobs were going begging as a result of a lack of takers.

Congressman Steve King, an Iowa Republican, asserted that "criminal aliens" accounted for more than a quarter of the jail population, although government figures show that immigrants make up 2 per cent of prisoners.

CNN's Lou Dobbs, a persistent advocate of immigration controls, said "illegal aliens" brought in 7000 new cases of leprosy over a three-year period, but government figures, showed there were between 200 and 250 new cases a year.

"The reason that [politicians] can make these claims with a straight face is they have virtually a buffet of options [drawn from] opinions masquerading as studies," said Demetrios Papademetriou, the president of the non-partisan Migration Policy Institute. "They can pick and choose from whatever is out there, but the truth, or serious analysis is taking a beating."

- Reuters