According to a 1998 article in The National Academies Press, "many [previous studies] represented not science but advocacy from both sides of the immigration debate...often offered an incomplete accounting of either the full list of taxpayer costs and benefits by ignoring some programs and taxes while including others", and that "the conceptual foundation of this research was rarely explicitly stated, offering opportunities to tilt the research toward the desired result."
A survey conducted in the 1980s found that economists themselves overwhelmingly viewed immigration, including illegal immigration, as positive for the economy. They found that 76 percent felt that recent illegal immigration has a positive affect on the economy.
In an article that appeared in the World Policy Journal (1994), Peter Andreas asserts that constraining the flow of illegal immigration in states such as California, may result in economic stagnation.
 Participation in the free market
One of the largest drivers of immigration both legal and illegal is economic supply and demand for labor and the natural human desire of people to participate in the economy and in so doing better their economic situation. Labor is a mobile economic factor of production, efforts to limit its mobility are attempts at limiting the free market (for labor). However, a free migration argument consistent with free market economy would require us to first have a free market and no welfare system.
According to the executive vice president of Banco Popular, the bank has found no higher rate of default in home loans to illegal immigrants than any other market the company serves.
 Impact on Social Services
The nonpartisan Congressional Budget Office. reviewed 29 reports published over 15 years to evaluate the impact of unauthorized immigrants on the budgets of state and local governments. It found the following
State and local governments incur costs for providing services to unauthorized immigrants and have limited options for avoiding or minimizing those costs The amount that state and local governments spend on services for unauthorized immigrants represents a small percentage of the total amount spent by those governments to provide such services to residents in their jurisdictions The tax revenues that unauthorized immigrants generate for state and local governments do not offset the total cost of services provided to those immigrants Federal aid programs offer resources to state and local governments that provide services to unauthorized immigrants, but those funds do not fully cover the costs incurred by those governments. Editorialist Robert Samuelson points out that poor immigrants strains public services such as local schools and health care. He points out that "from 2000 to 2006, 41 percent of the increase in people without health insurance occurred among Hispanics", although he makes clear that these facts are true of legal as well as illegal immigrants. According to the Center for Immigration Studies, 25.8% of Mexican immigrants lived in poverty — more than double the rate for natives in 1999. In another report, The Heritage Foundation notes that from 1990 to 2006, the number of poor Hispanics increased 3.2 million, from 6 million to 9.2 million.
Professor of Law  writes that the belief that undocumented migrants are exploiting the US economy and that they cost more in services than they contribute to the economy is "undeniably false". Lipman asserts that "undocumented immigrants actually contribute more to public coffers in taxes than they cost in social services" and "contribute to the U.S. economy through their investments and consumption of goods and services; filling of millions of essential worker positions resulting in subsidiary job creation, increased productivity and lower costs of goods and services; and unrequited contributions to Social Security, Medicare...