Advocates of more lenient immigration policies also disagree with the purely fiscal approach. Simply weighing tax receipts against public spending doesn't show the full picture, they say, since illegal immigrants also create tremendous economic value.
"Illegal immigrants are good for our economy," says IPC's Sefsaf. "They make our labor force and our economy bigger. Sure, you could kick them all out, but then you would have to shrink the economy."
Sefsaf also doesn't buy the traditional argument that illegal immigrants are stealing U.S. jobs: most legal residents work in middle-rung jobs and would not want to take low-paying jobs as fruit pickers or nannies.
After weighing the financial pros against the cons, she says the U.S. economy comes out slightly ahead due to the presence of illegal aliens.
Jeffrey Passel, a senior demographer at the Pew Hispanic Center, takes the debate one step further. He points out that most attempts to find a meaningful number are usually futile, since the data are so difficult to collect. And anyway, he says, what is the point?
"We don't generally ask these questions about anybody else," says Passel. He points out that using the "cost" argument, one could make a case against parents who generally benefit more from public schools than the taxes they pay. "It's not a subject that there is a definitive answer to."