Some Republicans think immigration reform is too lax. Nope; it is not nearly lax enough.

The comprehensive overhaul unveiled by the Senate's gang of eight has some commendable elements, such as prioritizing merit-based visas and clearing the backlog of legal applicants. But it also calls for another $7 billion in enforcement through drones, more fencing, an additional 3,500 (!) federal border agents, a national employer mandate, and an entire new bureaucracy—the Bureau of Immigration and Labor Market Research—most of which would have to be in place before the first undocumented resident could get the first green card.

This might have been necessary to mollify the nation's immigration hawks, who moderately support legal immigration but fiercely oppose the illegal kind. Politics is the art of the possible. Yet it's worth pointing out that the hawks are wrong.

Suppose you grow up poor in Alabama. You decide to move to New York to make a better life for yourself. But when you get to the state line, you're stopped by armed men who won't let you in. New York already has enough people, they say, and it doesn't need you. And since you weren't born there, you have no right to go there. You would—quite reasonably—find this ridiculous. So why is it any less ridiculous to tell a Guatemalan or a Bangladeshi that he cannot move to the U.S.?

Immigration hawks will say moving from Alabama to New York without permission is not against the law, but moving from Guatemala to the U.S. is. Case closed.

But it isn't. As Boston Globe columnist Jeff Jacoby points out in a piece on Martin Luther King's "Letter from Birmingham Jail," the rule of law is an important thing—but it is not the only thing: "The mindless enforcement of bad laws is not a substitute for decency or justice."

Decency and justice demand an immigration policy vastly more open and forgiving than either current policy or the senators' consensus proposal. Go back to the moving-to-New-York scenario above, which is a modified version of the introduction to an essay by Bryan Caplan in the Winter, 2012, issue of Cato Journal. Both scenarios establish what Caplan, a professor of economics at George Mason University, calls a moral presumption in favor of open borders.

Caplan points to research suggesting open borders "would roughly double world GDP, enough to virtually eliminate global poverty." If so, then the "harm that immigration restrictions prevent has to be at least comparable" to the harm they cause. What's more, we also need proof "that there is no cheaper or more humane way to mitigate the evils of [unrestricted] immigration."

Caplan then examines each of the standard reasons for strict immigration limits. For example, do they protect American workers? Not nearly so much as immigration hawks assume. While "low-skilled wages are indeed likely to fall" if the fences come down, "most Americans are not low-skilled" while "most of the world's would-be immigrants are, at best, substitutes for American high-school drop-outs."

What's more, "natives speak much better English," and "when immigration increases, native workers really do responed by switching to more language-based occupations, escaping lower pay for their physical skills and capturing higher pay for their language skills. . . . [T]his mechanism cuts the estimated effect of immigration on low-skilled natives' wages by 75 percent."

But even if you assume otherwise, Caplan says there are much cheaper and more humane ways to protect American workers than forbidding entry to foreigners. For instance, "charge immigrants surtaxes" and then "use the extra revenue to compensate low-skilled Americans."

Don't many immigrants come to the U.S. to mooch off our welfare state? Not as much as the hawks would have you think: "Welfare states focus on the old, not the poor." (If you're not sure that's right, compare Medicare's 2012 budget of $555 billion with the 2012 food-stamp budget of $78 billion.) And "since immigrants tend to be young, they often end up supporting elderly natives rather than milking the system."

In the rest of the paper, Caplan shows how each objection to immigration either does not have a factual basis, or could be handled through measures short of border quotas. In any event, the human harm from immigration is far less than the human harm imposed by immigration restrictions. He cites philosopher Michael Huemer, who presents the case of an individual—Marvin—who is in danger of starvation.

It is one thing, Huemer says, simply to not give Marvin food. In that case you are not killing him, you are letting him starve, and there is a moral difference. But suppose you "actively and forcibly restrain Marvin" from buying food from a willing seller, and Marvin starves. In that case you could be said to have done "something morally comparable to killing him."

That is just what immigration limits do. Countless impoverished people around the globe want to move to the U.S. and, as Caplan says, "millions of American landlords, employers, and stores would be happy to house, hire, and feed them. For the U.S. government to criminalize these transactions . . . is not merely uncharitable. It is unjust."

Republicans who genuinely believe in liberty and limited government will have to agree.

This article originally appeared at The Richmond Times-Dispatch.