The United States has always been a nation of immigrants, at our best when welcoming to our shores those who "yearn to breathe free." Indeed, immigration has had many positive effects on our economy and society. We have successfully, if not perfectly, lived out our motto of "out of many, one." We have had a culture and limited government that encouraged individual initiative, patriotic assimilation, upward mobility and hard work, all while allowing the economy to flourish through the free enterprise system. Today, unfortunately, things are different.

The problem is not a lack of law-abiding, hard-working people who want to make America their home. Right now there are some four million people waiting in other countries, trying to come to America lawfully.

While these would-be immigrants languish in our broken system, a bipartisan "Gang of Eight" senators unveiled their proposals Tuesday for a massive, comprehensive immigration bill, which was written and debated behind closed doors. Those in the room, including big business, big labor, and representatives of unauthorized immigrants, will all benefit in various ways from legislated amnesty.

What about the forgotten and hard-working American taxpayers? What about the promise of opportunity for all of the hard-working, naturalized American citizens who immigrated to America by following our laws?

The fact is that our modern welfare state has completely changed the equation on costs and benefits of low-skilled immigration. Our welfare system is costly -- approaching nearly $1 trillion a year -- and, even worse, includes perverse incentives, stifles upward mobility, weakens our work culture and has changed the whole immigration arithmetic.

Today, a single parent can get benefits from government totaling nearly $20,000 without working at all. James Pethokoukis at the American Enterprise Institute calculated that a single mother of two children earning $29,000 and getting welfare benefits would be financially better off than if she took a new $69,000 a year job and lost her government benefits.

Before lawmakers proceed with "comprehensive" reform, it is critical for them to understand the costs to taxpayers of an amnesty that qualifies millions of unauthorized immigrants for federal benefits.

The Heritage Foundation's Robert Rector has pioneered research into the cost to the federal government over time of granting amnesty. Rector was the driving force behind welfare reform in the 1990s. Five years ago, Rector found that amnesty would likely cost taxpayers some $2.5 trillion. Over the last six months he has been putting the finishing touches on an updated study that calculates an even higher price tag.

Some may say we can solve this fiscal problem by granting amnesty without any government benefits. We all know that will never happen. As soon as any of the nearly 11 million unauthorized immigrants are given legal status, the political fight will turn to speeding their transition to citizenship and promises of a full array of federal benefits.

Delaying eligibility for federal benefits to newly legalized immigrants merely puts off the day of reckoning. The truly enormous costs come when unauthorized immigrants start collecting retirement benefits. Social Security, Medicare, food stamps and other entitlement programs already impose huge, unfunded liabilities on taxpayers; adding more recipients only makes the fiscal hole we find ourselves in much deeper.

An amnesty of more than 10 million unauthorized immigrants will add significant costs to taxpayers because of the simple fact that, on average, today's unauthorized immigrants have the equivalent of a 10th-grade education. Those with that education level, whatever their background, tend to collect much more in benefits than they pay in taxes. And that means that the fiscal burden on Americans only gets heavier with amnesty. We cannot afford a policy that will add trillions of dollars to our long-term fiscal deficit.

Congress should fix our broken legal immigration system before considering giving unauthorized residents citizenship and federal benefits. This reform should be done in a step-by-step, open process that will win the trust of the American people.

One step would be to ease entry for college graduates (especially those who study in America on student visas) and investors. Surely we can all agree that these immigrants will grow our economy, create jobs and help our fiscal outlook. This is just one example of how immigration reform could proceed as a measured set of approaches tailored to the specific immigration problems rather than through backroom, "comprehensive" legislation guided by special interests.

In this immigration debate, we should encourage lawful immigration and discourage unlawful immigration. A critically important factor will be calculating the cost of amnesty to taxpayers. Any reform legislation should first do no harm to our already dire fiscal outlook.

-Former senator Jim DeMint is the president of The Heritage Foundation. Derrick Morgan is Heritage's vice president for domestic and economic policy.