The Atlantic profiles Vipul Naik, Michael Clemens, Michael Huemer, and other champions of free migration.  Highlights:

What if there was a program that would cost nothing, improve the
lives of millions of people from poorer nations, and double world GDP?
At least one
economist says that increased mobility of people is by far the
biggest missed opportunity in development. And an informally aligned
group of advocates is
doing its best to make the world aware of the “open borders”
movement, which suggests that individuals should be able to move between
countries at will.

Vipul Naik is the face, or at least the voice, of open borders on the Internet. In March 2012, he launched Open Borders: The Case,
a website dedicated to the idea. Naik, a Ph.D. candidate in mathematics
at the University
of Chicago, is striving for “a world where there is a strong
presumption in favor of allowing people to migrate and where this
presumption can be
overridden or curtailed only under exceptional circumstances.” Naik
and his two primary co-writers, Nathan Smith and John Lee, parse
research into
immigration impacts, answering claims by those they call
“restrictionists”–people who argue against open borders–and
deconstructing writings on migration
by economists, politicians, journalists, and philosophers.

And:

According to Clemens, we are all victims of an epic intuition fail.
“Development is about people, not places,” he has said many times over,
and often the
best way to make a person richer is by allowing them to move to
another place. We don’t really care about helping poverty-stricken
Liberia, we care about
helping poverty-stricken Liberians. It sounds almost too simple at
first: A very large percentage of people who have gone from extreme
poverty to
relative financial stability have done so by moving across borders.
So why don’t we just let more people move?

In 2008, Clemens and his frequent co-writer, Harvard economist Lant Pritchett, came up with a new statistic called “income per natural.”
Their goal was to show “the mean annual income of persons born in a
given country, regardless of where that person now resides.” They found
that large
percentages of people from Haiti, Mexico, and India who live above
international poverty lines don’t actually reside in their home
countries. “For example,
among Haitians who live either in the United States or Haiti and
live on more than $10 per day–about a third of the U.S. ‘poverty’
line–four out of five
live in the United States,” Clemens wrote.

Don’t miss John Lee’s appeal to Mark Zuckerberg:

I asked John Lee, a regular contributor to the
Open Borders site, what someone with unlimited money should do if
they want to convince people to support open borders. Mark Zuckerberg,
for example.

“The four words, ‘I favor open borders,'” Lee told me. “That would
be the biggest thing he can do. You really need to de-radicalize the
idea.”